The Messenger of Allah (S.A.W.) said: Allah the Almighty has divided people into two groups, holding us as the best of the two, for He has talked of Ashabal-Yamin (the companions of the right hand) and Ashab al-Shimal (the companions of the left hand). I am of the Ashab al-Yamin and of the best of them. Then Allah divided these two groups into many one thirds and held me as the best of the three, by these words: "And companions of the right hand", and those Foremost (in faith) will be Foremost (in the Hereafter).
I am among the Foremost and the best of them. Allah has further divided these many one thirds into tribes and placed me in the best tribe; and here is what he said: "And made you into nations and tribes, that ye may know each other. Verily the most honoured of you in the sight of Allah is the most righteous of you. And Allah has full knowledge and is well-acquainted (with all things)" (49:13). And I am the most righteous and the dearest with Allah without feeling any conceit. Then Allah comparted the tribes and put me in the best compartment; and this is what the Lord said: "And Allah only wishes to keep away all abomination from you, ye members of the family, and to purify you with thorough purification" (33:33). So, I and my Ahl al-Bayt are always away from sins.
Al-Imam Ali (A.S.) said: Allah has ordered obedience of the Messenger of Allah (A.S.) said: Allah has ordered obedience of the Messenger of Allah (A.S.) since he is infallible and pure and does not enjoin Allah's disobedience. Allah has ordered obedience of those charged with authority, for they are infallible and pure and do not enjoin His disobedience.
Al-Imam al-Baqir (A.S.) said: We can not be described; How can a group be recognized whom Allah has kept away abomination- i.e. doubtfulness-from?
Al-Imam al-Reza (A.S.): The Almighty Allah has bestowed Imamate on Ibrahim the Khalil as the third in rank after prophethood and friendship and made it nobility granted to him and praised him saying "I will make thee an Imam to the nations." Ibrahim said jubilantly: "And also (Imams) from my offspring?" And Allah replied: But my promise is not within the reach of evildoers (2:124)." Thus, this ayah excludes the Imamate of any evil doer up to the Day of Resurrection, and it will only be given to the chosen ones.
Then Allah honored him by ordaining Imamate in his pure and chosen offspring and said: "And We bestowed on him Isaac and, as an additional gift, (a grandson), Jacob, and We made righteous men of every one (of them). And We made the leaders, guiding (men) by our Command, and We sent them inspiration to do good deeds, to establish regular prayers, and to practice regular charity; and they constantly served us (21:27, 73)".
Al-Imam al-Hadi (A.S.) - in Ziyarat-i Jamiah by reading which visitation of Holy Imams is performed: I bear witness that you are rightly guided Imams and infallible and honored guided ones whom Allah has secured from any slippery; safeguarded against sedition; kept you away from abomination; purified you, and made you quite spotless.
Reasoning on the Characteristic State of Purity
It was pointed out before that purity (taharah) is the absolute feature of the Ahlal-Bayt (A.S.) underlying characteristics which make them competent for guiding and leading the Islamic community. Thus being rated as on top of all their other features and frequently referred to as reasoning for proving their rightfulness against those who had violated their rights.
In the event of Saqifa and refusing to pledge allegiance to Abu Bakr, al-Imam Ali (A.S.) while enumerating his own virtues addressed the former: I swear you to Allah [to admit] whether on the day of Kisa I and my family were included in the Holy Prophet's (S.A.W.) supplication or you, when he said, "These are my family, may they be on the path toward You, not toward the Fire." Abu Bakr said in reply: you and your sons.
Similarly, in the event of Fadak to prove Fatima's (A.S.) rightfulness, Ali (A.S.) addresses Abu Bakr: Tell me for whom the noble ayah: "And Allah only wishes to keep away all abomination from you, ye Ahl al-Bayt and make you pure and spotless, "was revealed concerning; us or others? Concerning you, said Abu Bakr.
Also, when a council was formed by the order of Umar to select a Caliph after him, al-Imam Ali (A.S.) referred to ayah of Tathir to prove his competence and addressed the council as follows: I swear you by Allah! Is there anybody among you about whom the ayah of Tathir has been revealed? They replied: No.
During the Caliphate of Uthman a group of Muhajir and Ansar gathered in the Mosque of the Holy Prophet (S.A.W.) telling their own virtues. They asked al-Imam Ali (A.S.) too to relate something.
Confirming their contributions to Islam, he made a reference to the event of Kisa and the ayah of Tathir.
Also in the event of the Nakithin revolt and the Jamal war-mongers, when al-Imam Ali(A.S.) called them to renew their allegiance, he referred to the trait of purity while counting his virtues to prove his rightfulness and said: Lo! We are the Ahl al-Bayt whom Allah has kept away any abomination from and made quite pure and spotless.
He also asserts the same feature in a letter to Mu'awiya ibn Abi Sufyan: We are a family from whom Allah has kept away all abomination and has made pure and spotless. And in the event of Battle of Siffin, when the two armies arrayed before one another, al-Imam Ali (A.S.) made a reference to the event of Kisa.
Similarly, his noble children, both those who were present in the event of Kisa like al-Imam al-Hasan(A.S.) and al-Imam al-Husayn(A.S.) and the ones who were not, like al-Imam Zayn al-Abidin(A.S.), al-Imam al-Baqir(A.S.) and al-Imam al-Reza (A.S.), have referred to the event of Kisa and the ayah of Tathir in proving the rightfulness of Ahl al-Bayt. The Holy Prophet's (S.A.W.) noble wife and a group of his companions such as Ibn Abbas, Sas ibn Abi Waqqas, and Wathilat ibn Asqa have in various instances referred to the purity of Ahl al-Bayt.

Source: The Image of Ahl al-Bayt (A.S.) in The Qur'an and Hadith
By: Muhammadi Rayshahri