Imam al-Sajjad (A.S.) in his advising letter to Muhammad Ibn Muslim al-Zuhri: May Allah keep the calamity far from me and you and have mercy on you and keep you away from the fire of Hell, because you are entangled in a state that you need mercy. Allah's bounties are so much for you that you are healthy and have lived a long life. Your responsibilities are more serious because [the Holy Qur'an] and the Holy Prophet (S.A.W.) are well known to you and you are also aware of the religion. You do have a duty to perform for each of his bounties and have a responsibility. He wishes no more than trying your gratitude and reveal His kindness to you. He has said: "If ye are grateful, I will add more (favours) unto you, but if you show ingratitude, truly My punishment is terrible indeed"(14:7).
Behold then what sort of a person you will be on Resurrection Day, when you would stand in Allah's presence and He would ask you about His bounties and about how you performed your duties toward Him. Never suspect that Allah will accept your excuses or will consent to your shortcomings well. Away! Far from it! He has taken vow from the learned in the Holy Qur'an when He says: "And remember Allah took a covenant from the people of the Book to make it known and clear to mankind, and not to hide it"(3:187).
Remember that the heaviest burden you carry, and the slightest truth you've concealed is your approaching the tyrant and accepting his invitation when he was alone. You accompanied him to help him to go astray. Vow! How much I fear that you will be punished with the treacherous and will be reckoned for your actions. You have received the things which were not yours, and have been close to those who did not give the people what was due to them. When you were close to such people, you've not prevented any wrong-doing. You've taken for friends people who were against Allah. Is it not that their inviting you was to pave their ways to cruelties they committed? With your help they have done something that Muslims look at the true learned men with suspicion and doubt; and you caused the ignorant follow them. [Even] their strongest friends and their most powerful companions couldn't justify their wrong -doings as effectively as you did. How little you've gained from them compared to what they've taken from you. How unworthy are the things you've received in return to what they have taken from you [your faith].
Be constantly attentive to your soul! No other person would do that for you, and attend to your soul like a responsible person. See how you thank the One who brought you up from childhood to maturity. How much I fear that you would be among those people about whom Allah has said in His Book: "After them succeeded an (evil) generation: They inherited the book, but they choose (for themselves) the vanities of this world, saying (for excuse) everything will be forgiven"(7:167). You do not live in a long-lasting abode; you are in an abode from which you shall be departing soon. How much longer one lives after his fellow creatures?! Blessed is a man who lives in this world fearfully and woe to a man who would die unrepentant. Beware, as you've been informed; therefore make haste as your time is limited. You deal with the One who is not unaware and is always watchful on you. Be prepared as you will have a long journey soon, and find a remedy for your sins, as you have come down with a serious disease.
Do not suspect that I have the intention of reproaching you, but I wish that Allah would give you back your lost faith, and revive your thinking faculty, and remind you of the words of Allah the Exalted when He says in His Book: "But remind (them); for remembrance benefits the believers" (51:55).
You've forgotten your lost companions, and are like a ram with one broken horn. See if the others have been subjected to the same calamity as you have; or do you think that you know some thing which they did not know? You've benefited a status and position that made people love you and follow your ways and obey your orders. If you consider something legitimate, others will consider it legitimate too, whereas you are not merited for this.
But their love is towards what you do posses [knowledge] their scholars have gone and the dominance of ignorance is on you and them your and their love of the world make them follow you as well. Haven't you seen that how much you, yourself are unaware, and ignorant; and how much the people are seditious and are entangled in calamity? There is no doubt that you have caused such calamities; and prevented the people from doing their routine daily works. All these people are eager to reach the status equal to that of yours, or reach to whatever you've reached. It is because of you that they've fallen into a fathomless sea and are thus in trouble. May Allah come to our relief; and it is only from him that we should seek help.
Now divert your attention from the situation you are in, so as you might join the worthy people who are hidden in their shabby and worn out clothes. [Because of hunger and fasting] they are on the verge of starving to death and there is no veil between them and Allah. The world would not deceive them and they would not be infatuated with the world either. They asked and required [heavenly rewards] and it didn't take a long time for them to attain it. When the world deals with you who are learned and approaching your death, how can a young person who has not the knowledge and his thinking and reasoning faculties are not matured, be immune?! "To Allah we belong, and to Him is our return (2:150). Where should we find support? And whom should we apologize? We complain to Allah of our sorrows and sufferings which you've made for us. We expect a reward from Him for all those sufferings.
See how you express your gratitude toward the One who has nurtured you in your early years and when you were grown up? And how do you revere the One who has made you well reputed among the people? And how do you keep the robe of honor which protects you? And how is your relation to the One who has ordered you to be close to Him and be humble and obedient to Him? What has happened to you that you do not awake and repent of your sins and offences and say:
"I swear to Allah that I have not taken even one step to revive a religious law, or to prevent doing a wrong action". This, in itself, is a form of gratitude to the One who has given you this knowledge. How much I fear that you would be considered one of those about whom Allah has said "But after them there followed a posterity who missed prayers and followed after lusts, soon then will they face destruction" (19:59). Allah has entrusted His book and knowledge to you, but you failed to do your responsibility.
Praise be to Allah that has kept us safe from what has befallen on you. Wassalam.

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