Muslim scholars differ in answering two questions pertaining to the companions of the Messenger of God:

1. Who are the companions of the Prophet Muhammad?
Most of the Sunni scholars consider all those who adopted Islam during the time of the Prophet, saw the Prophet, and prayed with him to be of his companions. However, it seems that the Messenger himself did not agree with these scholars. Al-Tabari in his History part 3, page 68, reported that there was an argument between Khalid Ibn Al-Walid and Abdul Rahman Ibn Awf when Khalid killed some members of Banu Jadhimah. The Messenger of God sent Khalid as a missionary for Islam (not as a fighter). Khalid exceeded the order of the Messenger and killed a number of men from Banu Jadhimah after he gave them the assurance of no-harm.
Some men from Banu Jadhimah had killed Al-Fakih Ibn Al-Mughirah Al-Makhzumi, uncle of Khalid, and Awf Ibn Abd-Awf, father of Abdul Rahman, before the conquest of Makkah. Now Khalid acted in revenge in spite of the Prophet's orders. In their heated dialogue, Abdul Rahman said to Khalid: "You followed the method of the pre-Islamic era." Khalid said:
"I only avenged the killing of your father." Abd Al-Rahman:
"You lie. I already killed the killer of my father, but you avenged the killing of your uncle." Their heated argument led to a verbal abuse on the part of Khalid. When the Prophet found out about it, he said to Khalid: "...Khalid, leave my companions alone. By God, should you have a piece of gold the size of Uhud Mountain, and you spend it in the path of God, your charity would not compare to a morning or evening trip in defense of Islam by any one of my companions." (Ibn Hisham, in his Sirat of the Prophet, part 2, page 421).
This statement of the Prophet indicates that Khalid was not considered a companion of the Prophet because he told him to leave his companions alone. Thus, the Prophet clearly indicated that Khalid is not one of his companions. Yet, this statement was uttered by the Prophet after the conquest of Makkah (which took place two years after Khalid adopted Islam, shortly after the pact of Al-Hudaybiyyah). The exclusion of Khalid from the community of the Prophet's companions means the exclusion of thousands of companions who adopted Islam during the time of the Prophet, who met the Prophet, and who prayed behind him.

2. Are all Companions of the Prophet Righteous?
The righteousness of all the companions and their worthiness of confidence are matters about which the Shi'ites and the Sunnis argue. The majority of the Sunni scholars believe that all the companions are righteous and worthy of our confidence.
The Shi'ite scholars are selective. The Sunni scholars cite Qur'anic verses for substantiating their claim: "Muhammad is the Apostle of God; and those who are with him are firm against unbelievers, compassionate towards one another. You see them bowing and prostrating, seeking grace from God and His satisfaction ... The mark of prostration shows on their faces... Allah has promised those among them who believe and do righteous deeds forgiveness, and a great reward." (ch. 48. v. 29)
Thus, the Almighty described the companions of the Messenger as firm against the unbelievers, merciful among themselves; and that they bow and prostrate. The mark of their prostration shows on their foreheads; and that Allah promised those who believe and do righteous deeds forgiveness and a great reward.
All these descriptions substantiate the piety and virtue of the companions. The verse, however, does not include all the companions. It only includes the companions who were firm against the unbelievers, merciful among themselves. Thus, the companions who were not firm against the unbelievers or were unmerciful to the believers would not be included by the verse. It would be only logical to say that those who shed the blood of Muslims without justification in civil wars such as Talhah, Zubayr, and Mu'awiyah are not included in this Qur'anic statement, plus all companions who joined them in their unrighteous wars against Imam Ali, and those who divided the Muslims and destroyed their unity.
Furthermore, the end of the verse clearly indicates that the praise was not to include all the companions because it declares that only those who believed in Islam and did good deeds will be entitled to forgiveness and great rewards. One of the verses which is offered as evidence of the righteousness of all the companions of the Prophet is the following: "And the early Muslims from the Makkan migrants and the Madinite Ansar (the helpers) and those who followed them with their good deeds, Allah is well pleased with them, and they are well pleased with Him; and He has prepared for them gardens beneath which rivers flow, to dwell therein forever. That is the mighty achievement." (ch. 9, v. 100)
This verse, however, speaks of the virtue of the migrants and Madinites who adopted Islam at the early state of the Islamic era. Thus, it does not include the thousands of the companions who adopted Islam after the Hudaybiyyah truce or after the conquest of Makkah. These were not from the early Muslims. Their Islam took place about twenty years after the proclamation of Islam and about eight years after Hijrah. Another verse which is cited for the righteousness of all companions is the following:
"Allah was well pleased with the believers when they swore allegiance unto thee beneath the tree; He knew what was in their hearts, and He sent down tranquility to them and rewarded them with a speedy victory..." (ch. 48, v. 18) This verse also does not include all the companions who declared their Islam after signing the Hudaybiyyah pact which took place during the sixth year after Hijra.
The declaration of the allegiance to the Prophet under the tree took place shortly before signing the pact. The companions who gave allegiance under the tree at Hudaybiyyah were about fourteen hundred. It is worthy to mention that a number of students of the companions (such as Sa'id Ibn Al-Musayyab and Al-Shi'abi and Ibn Sirin) said that the early migrants were those who prayed to the two Qiblas (Al-Masjid Al-Aqsa and Al-Ka'bah). (Abu 'Umar Yusuf Ibn Abd-Barr, Al-Isti'ab part 1, pages 2-3)

Do The Hadiths Of The Prophet Substantiate The Righteousness Of The Companions
Some scholars tried to substantiate the righteousness of the companions through a number of hadiths:
l. It is reported that the Messenger of God said, "None of those who attended the battle of Badr or the pact of Hudaybiyyah will enter Hell."
2. It is also reported that the Prophet said: "None of those who gave their allegiance under the tree (during the event of Hudaybiyyah) will enter the Fire." (Ibn Abd al-Barr, page 4) The two hadiths do not substantiate the righteousness of any companions except the companions who were present at Badr and Hudaybiyyah. Putting them together, their number would not reach two thousand, while the number of the companions was much bigger.
Those who attended the conquest of Makkah were ten thousand, and those who went with the Prophet to Tabuk were about twenty-five thousand. Thus, the majority of the companions of the Prophet would not be included in these two hadiths.

The Opinions of The Selectionists
The Shi'ite Muslim scholars did not put all the companions in one rank; nor did they say that all of them were righteous. Some of them were righteous to the highest degree. Some of them were truthful and worthy of confidence, but they were not entirely righteous. Some of them were not known to be righteous or unrighteous, and some of them were known to be devious.

Qur'anic Verses Support The Selectionists
These scholars who view that some of the companions were neither righteous nor in a place of confidence support their view with a number of Qur'anic verses:
"And they say: 'obedience'; but when they leave thee, some of them spend the night planning other than what they say to you. Allah records what they plan by night. Disregard them and put thy trust in Allah. Allah is Sufficient Trustee." (ch. 4, v. 81) This verse declares that a number of those who were residents of Madinah were Muslims, and they prayed with the Prophet and attended his gatherings and heard the Messenger commanding the Muslims to do some good deeds. They used to say to the Prophet: "We heard you and we will obey you;" but when they left him, they did not obey the Messenger.
We find in chapter nine of the Holy Qur'an many verses which indicate that some of the companions of the Messenger were people of hypocrisy, and the Messenger did not know their hypocrisy.
"And among those around you of the wandering Arabs are hypocrites and among the people of Madinah there are some who persist in hypocrisy whom thou (0 Muhammad) know not. We know them and We shall chastise them twice; then they will be relegated to a painful doom." (ch. 9, v. 101) "O Prophet! Combat the disbelievers and the hypocrites and be hard on them. Their abode is Hell, a hapless journey's end. They swear by Allah that they said nothing (wrong), yet they did say the word of disbelief. They disbelieved after they declared their Islam, and they plotted that which they could not carry out, and they sought revenge only because Allah and His Messenger enriched them of His bounty..." (ch. 9, v. 73)
"Among them are men who made a covenant with Allah (saying): If He gives us of His bounty we will give alms and become of the righteous. Yet, when He gave them of His bounty, they hoarded it and turned away, averse. So He made a consequence (to be) hypocrisy in their hearts until the day when they shall meet Him, because they broke their word to Allah and because they lied." (ch. 9, vs. 75-77)
We also find in chapter 33, "The Confederates": "And when the hypocrites and those in whose hearts is a disease say 'Allah and His Messenger promised us nothing but delusions.' And when a party of them said:
'Oh folk of Yathrib! There is no stand possible for you; therefore, go back.' And some of them even ask permission of the Prophet, saying: 'Our homes are exposed to the enemy, and they lay not exposed.' They only wished to flee." (ch. 33, vs. 12-13) The chapter of Al-Munafiqun is a clear evidence that a number of Muslims (who declared their Islam at the time of the Prophet, and lived with him in Madinah, and prayed with him, were hypocrites. They came to the Prophet to defend themselves by taking an oath in the presence of the Prophet that they did not betray him, and they were liars.
They had believed in Islam then deserted it and Allah sealed their hearts. "When the hypocrites come to thee (O Muhammad), they say: 'We bear witness that thou art indeed Allah's Messenger. And Allah knows that thou art indeed His Messenger, and Allah bears witness that the hypocrites indeed are speaking falsely. They made their oaths a shield so that they may turn (men) from the way of Allah. Verily, evil is that which they wanted to do. That is because they believed and then disbelieved; therefore, their hearts were sealed so that they understand not.' " (ch. 63, vs. 1-3)
These numerous verses which are in many of the Qur'anic chapters testify clearly that many of the people who declared Islam during the time of the Prophet, and who lived and prayed with him, were hypocrites. What testimony could be bigger than the testimony of the Qur'an? These hypocrites were living with the rest of the companions, and their names were not known. Therefore, it is impossible to avoid taking hadiths from them or know how many they were.
Historians, among them Al-Tabari in his History, part 2, page 504, and Ibn Hisham in his Al-Sirah Al-Nabawiyyah, part 2, page 64, reported that when the Messenger went with his army to Uhud, he had with him one thousand companions. But Abdullah Ibn Abi Salul left the Prophet and went back to Madinah accompanying three hundred from the Madinites. Islamic history did not inform us of the names of any of the three hundred except the name of their chief, Abdullah Ibn Abi Salul. Knowing that the situation was so, how can we avoid taking hadiths from these hypocrites, who were not separated from the good companions through any mark of distinction?

The Companions Who Shed The Blood Of The Muslims
We should not forget that there were among the companions some prominent men such as Talhah, Zubayr, Mu'awiyah, Amr Ibn Al-As, Al-Nu'man Ibn Bashir, and Samurah Ibn Jundab who shed Muslim blood. These should not be considered in a place of confidence after they shed the blood of thousands of Muslims in order to reach their worldly goals. Allah declared in His book the following:
"And whoever kills a believer deliberately, his reward is Hell forever, and the wrath of God is upon him, and He cursed him and prepared for him a great punishment." (ch. 4, v. 73) Thus, if a person kills a believer, his abode will be the Fire and the wrath of Allah is upon him, and He curses him and prepares for him a great chastisement. This will be the fate of people such as Mu'awiyah, Amr Ibn Al-As, Talhah, and Zubayr who shed the blood of more than forty-thousand Muslims.
It would be very illogical to consider people who committed so many sins righteous and their reports acceptable. There are people who say that these men who committed such sins are from the companions whom Allah likes, because they were from the early Makkan and Madinite Muslims, and they were among the ones who gave their allegiance to the Messenger under the tree of Hudaybiyyah.
These are from among the ones whom Allah was pleased with; and whoever Allah was pleased with one time, He will never be angry with. This would be clear when we look at the end of the verse which gives the early Muslims of Makkah and the Madinah the good tidings that they will have gardens under which rivers flow, wherein they will dwell forever. But this verse and the verse of allegiance under the tree of Hudaybiyyah did not include men such as Mu'awiyah and Amr Ibn Al-As because they were not from the early Muslims nor from the early migrants from Makkah to Madinah; nor were they from the people of the allegiance under the tree of Hudaybiyyah.
Amr Ibn Al-As adopted Islam after Hudaybiyyah and Mu'awiyah adopted Islam after the conquest of Makkah. Furthermore, we cannot find in the Qur'an any verse that declares that whomever God has been pleased with, God will not be angry with. It is inconceivable that Allah will give a permanent immunity against punishment to a person who did a good deed, such as being of the early Muslims or early migrants from Makkah to Madinah, and that Allah will forgive his shedding the blood of thousands of believers without any justification. If it were so, it would mean that a companion could cancel all the Qur'anic rules and the instructions of the Prophet. Certainly, we can not believe this when we remember that Allah said to His own Messenger Muhammad:
"Say: surely I fear (if I disobey my Lord) the chastisement of a grievous day." (ch. 6, v. 15) If a companion can interpret the Qur'anic verses and the Prophet's words the way he wants, he may be able to give a verdict that the five daily prayers are only desirable and not imperative.
He may say "I understand from Aqimu Al-Salat (offer prayer) that the prayer is only desirable. Nor do I understand from the word "salat" that it has to contain bowing and prostrating, or reading from the Qur'an or the declaration of the Shahadah. It would be sufficient in the prayer to supplicate the Lord to forgive or to give sustenance or to prolong life because the word Salat used to mean supplication before Islam.

The Messenger Of God Predicted The Deviation Of Many Of His Companions
The Messenger informed the Muslims that many of his companions will deviate after him. Al-Bukhari in his Sahih, part 2, page 149, reported that the Prophet said: "A number of my companions will come to drink from the basin. When I recognize them, they will be taken away from my sight. I would say: 'My Lord, these are my companions.' And Allah will say:
'You do not know what they innovated after you.' " The same source, page 150, recorded that Abu Hazim reported that Sahl Ibn Sa'd reported that the Prophet said: "I shall come to the Hawd (basin of water) before you. Whoever meets me there will drink water. And whoever drinks of it will never be thirsty afterwards. Groups will come to me, and I will recognize them and they will recognize me and they will be screened from me." Abu Hazim said: "Al-Nu'man Ibn Ayyash heard me and said:
'I testify that Abu Sa'id Al-Khudri said and I heard him adding to it the following: I will say: "May God put away from me whoever deviated after me.' " Similar to this is reported by Muslim in his Sahih, part 15, pages 53-54. Al-Bukhari reported in the section of Al-Hawd that Abu Hurayrah reported that the Messenger of God said: "On the Day of Judgement a group of my companions will come to the Hawd (Basin), and they will be prevented from drinking out of the basin. I will say: 'My Lord, these are my companions.'
He will say: 'certainly you do not know what they innovated after you. They deserted their religion.' " Al-Bukhari reported in his Sahih, part 4, page 169, that one reporter quoted Ibn Abbas as saying that the Prophet said: "You will be resurrected bare footed, unclothed, and uncircumcised." Then he read: 'As We started the first creation, We shall resurrect it, a promise on Our part. Certainly We shall fulfill it.' "
"Certainly a number of my companions will be taken to the left side, and I will say: 'My companions, my companions.' Allah will say:
'They continued deserting their faith after you left them.'" I will say as the good servant of God (the Messiah) said: "And I was a witness on them as long as I was with them..." Muslim in his Sahih, part 10, page 59, reported that the Messenger of God said: "I will be the first one to come to the Basin, and I shall be challenged about some people and I will lose them, then I will say: 'My Lord, these are my companions; these are my companions.'
I will be told: 'You do not know what they innovated after you.' "Muslim in his Sahih, part 10, page 64, recorded that Anas Ibn Malik reported that the Prophet said: "Men from among the people who accompanied me shall come (on the Day of Judgement) to the Basin. When I see them and they are brought to me, they will be taken away from me. I will say: 'My Lord, these are my companions.' It will be said to me: 'You do not know what they innovated after you' "