Some letters of the imam disclose an important side of the religious life which was confused at that age. The following are some of his letters to his adherents:

1. To Isaaq an-Naysaburi
Imam Abu Muhammad (a.s.) sent a letter to Isaaq bin Isma’il an-Naysaburi saying in it,
“May Allah protect us by His protection, and take care of you in all your affairs by His favor. I understood your letter, may Allah have mercy on you. We, praise be to Allah and by His blessing, are people of a house who pity our followers and feel delighted for the succession of the favors of Allah on them, and feel happy for every blessing that Allah the Almighty endows them with. O Isaaq, may Allah endow you with all blessings and endows whoever is like you whom Allah has had mercy on and given insight like yours…and may He determine the Paradise for you…
And I say: praise be to Allah as the best praise He has ever been praised with and forever for His mercy on you, His saving you from perishment, and smoothing your way on the obstacle. By Allah, it is insurmountable, impassable, difficult obstacle with great distresses that had been mentioned in the first Books. At the time of the deceased (Imam al-Hadi), peace be on him, and at my time you had done some things that neither I was satisfied with you nor were you right in them.
O Isaaq, know well that whoever comes out of this world blind will be blind in the afterworld and more astray. O Isaaq, it is not the eyes that become blind but the hearts that are in the chests. Allah says about the unjust, (He shall say: My Lord! why hast Thou raised me blind and I was a seeing one indeed? He will say: Even so, Our revelations came to you but you neglected them; and thus you shall be forsaken this day).[1] Is there a sign greater than the excuse of Allah on His creation, His trustee in His earth, and His witness on His people…after those who had left from his first fathers the prophets and his last fathers the guardians (peace and blessings of Allah be on them all). So where do you go astray and where do you go like beasts? You deviate from the truth and believe in falsehood and disbelieve in the blessings of Allah. Are you from those who believe in a part of the Book and disbelieve in the other? So what is the reward of him who does that from you and from other than you? It is but meanness in this life and eternal torment in the afterlife. By Allah, it is the great disgrace! When Allah imposed on you, by His favor and mercy, the obligations, He did not impose them on you because He was in need of you, but out of His mercy on You-there is no god but Him-to distinguish the good from the bad, and to try what there was in your chests, and test what there was in your hearts so that you would compete for the mercy of Allah and that your positions in His paradise would be one better than another. He imposed on you hajj, umrah (minor hajj), prayer, zakat, fasting, and the following of the Ahlul Bayt (a.s). He made to you a door by which you open the doors of the other obligations and as a key to His way. Except for Muhammad (blessings of Allah be on him), and the guardians from his progeny you would be confused like beast knowing nothing of the obligations. Is a town entered except from its gate? When Allah favored you by appointing the guardians after your prophet, He said, (This day have I perfected for you your religion and completed My favor on you and chosen for you Islam as a religion).[2] He imposed on you rights for His guardians and ordered you to carry them out so that your wives, properties, foods, and drinks would be lawful to you. Allah said, (Say: I do not ask of you any reward for it but love for my near relatives),[3] and know well that (whoever is niggardly, is niggardly against his own self; and Allah is Self-sufficient and you are the needy).[4] There is no god but Allah, and my speech became too long on what was for you and what was required from you.
Except for that Allah wanted to complete his favor on you, you would neither see a line from me nor would you hear a word after the leaving of the deceased (Imam al-Hadi), peace be upon him, while you are in inadvertence to your end, and after my appointing Ibrahim bin Abdah to you, and after my book that Muhammad bin Musa an-Naysaburi had brought to you, and Allah is He whose help is sought in any case. Beware to be unmindful towards Allah so that you shall be from the losers! Away with him he who turns his back to the obedience of Allah and does not accept the advice of His guardians! Allah has ordered you to obey Him, to obey His messenger, and to obey those in authority among you. May Allah mercify your weakness and inadvertence, and make you patient with your affair. What has beguiled man from his Lord?! If mountains understood some of that which was in this book, they would crack and split because of the fear of Allah, and turn back to the obedience of Allah. Do whatever you like (so Allah will see your work and (so will) His Messenger and the believers; and you shall be brought back to the Knower of the unseen and the seen, then He will inform you of what you did).[5] Praise be to Allah,
the Lord of the worlds, and His blessings be on Muhammad and all his progeny.”[6]

2. His letter to the people of Qum and Aabeh
Imam Abu Muhammad (a.s.) sent a letter, some parts of which were lost, to his Shia from the people of Qum and Abeh (Aveh) saying to them,“Allah the Almighty with His generosity and kindness has favored His people with His prophet Muhammad (a.s.) as a bearer of good tidings and a warner, and has made you succeed in accepting His religion, granted you with His guidance, and planted into the hearts of your past ancestors (may He have mercy on them) and your living offspring (may He suffice and make them live long) the love of the pure progeny (of the Prophet). They, who had left, left on the way of righteousness, and the path of truth and success, and they went to the place of successors, got the fruits of what they had sowed, and found the result of what they had done before…
Our intention is still firm, and our selves are satisfied with your good thoughts. The fixed relation between us and you are firm. It is a will that our ancestors and your ancestors had recommended, and a covenant that had been entrusted to our youth and your old men. They are still on their faith, and Allah has gathered us in the close relation, and close kinship. The Alim (peace of Allah be on him) said, ‘A faithful is a brother of a faithful from his father and mother…”[7]

3. His letter to Ali bin al-Husayn
Imam Abu Muhammad (a.s.) sent a letter to the famous jurisprudent Abul Hasan Ali bin al-Husayn bin Musa bin Babwayh al-Qummi, the notable of the Shia and prominent personality in Hadith, jurisprudence, and the rest of the Islamic sciences. Imam Abu Muhammad (a.s.) said in his letter,“Praise be to Allah the Lord of the worlds, and the end is for the righteous, the Paradise is for the monotheists, the Hell is for the atheists, and there should be no hostility except against oppressors, and there is no god but Allah the best of creators, and blessing be on the best of His creation Muhammad and his pure progeny.
O my sheikh, trustee, jurisprudent Abul Hasan Ali bin al-Husayn al-Qummi-may Allah be satisfied with you, and make from your progeny good children- I recommend you to fear Allah, offer prayers, and give zakat because no prayer is accepted from one who does not give zakat. I also recommend you to pardon others, suppress anger, continuously associate with kin, comfort brothers and try to carry out their needs at difficulty and ease, be patient, learn religion, be certain of things, undertake the Qur'an, behave with good morals, enjoin the good, and to forbid the wrong. Allah says, (There is no good in most of their secret counsels except (in his) who enjoins charity or goodness or reconciliation between people).[8] I recommend you to avoid all sins and vices. You are to keep on offering Night Prayer, for the Prophet (a.s) had recommended Ali saying to him, ‘O Ali, you are to keep on the Night Prayer.’ He repeated that three times. Whoever disregards the Night Prayer is not from us. Act according to my recommendation and order my Shia to act due to that. Wait for deliverance, for the Prophet (a.s) said, ‘The best deed of my nation is the waiting for deliverance.’ Our Shia shall be still in sorrow until my son, whom the Prophet (a.s) brought good news about, shall appear. He will fill the earth with justice and fairness after it has been filled with injustice and oppression. O my sheikh, be patient and order all my Shia to be patient; (Surely the earth is Allah's. He gives it as inheritance to whom He will and the end is (best) for the righteous).[9] Peace, mercy, and blessings of Allah be on you and on all our Shia, and Allah is sufficient for us; the best Protector is He, the best Patron, and the best Helper.”[10]

4. His letter to one of his followers
One of the Shia wrote to Imam Abu Muhammad (a.s.) telling him about the disagreement between the Shia. The imam replied to him in this letter,
“Allah has addressed reasonable people…people concerning me are in different classes; a discerning one is on the way of deliverance, keeping to the truth, clinging to the branch of the origin without being doubtful or suspicious, and finding no resort other than me. There is another class of people who do not take the truth from its owners; they are like a traveler in the sea. They wave whenever the sea waves, and calm whenever the sea calms. Another class of people are those who have been overcome by Satan. They just resist the people of truth, and fight truth by falsehood out of envy. So let alone whoever goes right or left, because when a shepherd wants to gather his sheep, he gathers them with the least effort. Beware of showoff and panting after authority because they lead to perishment…’[11]

5. His letter to another one of his followers
Imam Abu Muhammad (a.s.) sent a letter to one of his followers expressing his grief from some rabble of the Shia who had deviated from the right path. He said,
“No one of my fathers had been afflicted like what I have been afflicted with the suspicions of this group…if this matter (imamate) was a matter that you had believed in and kept on it until a certain time and then stopped, then suspicion would have certain case, but if it (imamate) is continuous as long as the affairs of Allah are continuous, then what is the meaning of this suspicion?...’[12]

6. His letter to Abdullah al-Bayhaqi
Imam Abu Muhammad (a.s.) sent the following letter to Abdullah bin Hamdwayh al-Bayhaqi:
“I have sent Ibrahim bin Abdah so that the (other) districts and the people of your district pay my dues on you to him and I made him my trust and agent before my followers there. Let them fear Allah and pay the dues and they have no excuse in not doing that or delaying it. May Allah not distress them for disobeying His guardians and may He have mercy on them and on you through my mercifulness to them, and Allah is Ample-giving, Generous.”[13]

7. His letter about Ibrahim
Imam Abu Muhammad al-Askari (a.s.) had appointed Ibrahim bin Abdah as his agent to receive the legal dues and to spend them on religion and on the needy, and given him a letter mentioning in it his reliability and high position. Imam Abu Muhammad (a.s.) was asked whether this letter was written by him or not, and he replied,
“My book that came to Ibrahim bin Abdah on appointing him as my agent to receive my rights from our followers there…yes, it was my book written by my hand to him. I have appointed him to them in their country. It is true and not false. Let him fear Allah as He should be feared, and let them take out my rights and give them to him, for I have permitted him to do with them as required. May Allah give him success and save him from failure.”[14]

8. His letter to his followers
He sent this letter to some of his followers:
“May Allah gift you with asceticism in this life and success as He pleases, assistance for His obedience, protection from disobedience, guidance from deviation, and may He gather for us and for our followers the good of the two abodes (this life and the afterlife).
I was informed of the disagreement of your hearts, and the separation of your desires, and the incitement of Satan until he caused separation among you, disbelief in religion, attempting to destroy what your ancestors had built in the religion of Allah and proved the rights of His guardians. He (Satan) took you to the way of deviation, and away from the path of the truth, and so many of you receded as if you had not read the Book of Allah and not understood any of His commands and prohibitions. I swear that if your fools rely on their delusions and fabricate false traditions, they shall deserve torment, and if you are satisfied with that from them and do not deny it by your hands, tongues, hearts, and intentions, you shall be participants with them in what they have fabricated against Allah, His messenger, and the guardians after him. If it was not so, the people of az-Zabad would not lie in their claim, nor al-Mughirah in their disagreement, nor al-Kaysaniyyah on their man, nor other liars and the deviants who have turned away from us. Indeed, you are worse than them…and most of them were obliged to submit to the command of Allah, except some group that if I want, I shall mention it by the name…Satan has overcome them and made them forget the mention of Allah, and whoever forgets the mention of Allah…Allah will throw him into Fire, and it shall be an evil abode.
My this book is an authority on them, and an authority for your absents on your presents, except one who is informed and carries out his duty. I pray Allah to gather your hearts on guidance, protect you by piety, and make you do what pleases Him, and peace, blessing, and mercy of Allah be on you.’[15]

9. His letter to one of his adherents
Imam Abu Muhammad (a.s.) said in this letter to one of his followers:
“Every predestined thing would come true. Rely on Allah the Almighty and He will suffice you, and trust in Him and He will not disappoint you! You have complained against your brother. Know well that Allah does not help in the rapture of relations, and Allah is over any oppression of every oppressor. Whoever is oppressed surely Allah will help him, and Allah is Strong, Mighty. You have asked me to pray for you. May Allah the Almighty keep you safe, and be your helper and protector. I pray Allah the Generous, Who has made you know His right and the right of His guardians that others than you were ignorant of, not to remove from you any blessing  He has endowed you with, He is Patron worthy of all praise.’[16]

10. His letter to one of his Shia adherents.
One of the Shia wrote a letter to the imam complaining against an oppressor who oppressed and did him wrong. Imam Abu Muhammad (a.s.) replied to him:
“We satisfy ourselves with Allah the Almighty this day against every oppressor, wrongdoer, and envier. Woe unto whoever says something that Allah knows its opposite. How terrible is that which he shall meet from the Master of the Day of Judgment! Surely Allah the Almighty is the Helper and Assistant to the oppressed. Trust and rely on Him and He will relieve your distress and save you from the evil of every evildoer. May Allah do that for you and favor us with you, He is powerful over everything. May Allah overcome every oppressor this moment! No one, who wrongs and oppresses, shall be successful. Woe unto whoever is taken by the fingers of the oppressed! Do not be distressed but trust in Allah and rely on Him, and He will bring your deliverance soon. Surely Allah is with those who are patient and who do good to others.’[17]

References
[1] Qur'an, 20:125-126.
[2] Qur'an, 5:3.
[3] Qur'an, 42:23.
[4] Qur'an, 47:38.
[5] Qur'an, 9:105.
[6] Tuhaf al-Uqool, p.484-486, Bihar al-Anwar, vol.78 p.374-377, Rijal al-Kashshi, p.354-357,.
[7] Bihar al-Anwar.
[8] Qur'an, 4:114.
[9] Qur'an, 7:128.
[10] Rawdhat al-Jannat, vol.4 p.273-274.
[11] Bihar al-Anwar, vol.78 p.370.
[12] Bihar al-Anwar, vol.78, p.372.
[13] Rijal al-Kashshi, p.358.
[14] Rijal al-Kashshi, p.358.
He has endowed you with, He is Patron worthy of all praise.’[16]
[15] Ad-Durr an-Nadheem, p.224.
[16] Ad-Durr an-Nadheem.
[17] Ad-Durr an-Nadheem, p.225.