It has been narrated that Imam Hasan Askari (AS) wrote a letter to one of the great scholars, namely Ibn Babeweyh1 (May Allah’s mercy be on him), saying:

“O! My trusted and experienced scholar, Abu al-Hassan Ali Ibn Qummi; may Allah give you success in His way. May Allah bless you with pious children. I advise you to piety, consistency on (your daily) prayers, and on paying alms. Indeed, the daily prayers will not be accepted of those who do not pay alms. I advise you to forgive people at the time of anger; visit your relatives and sympathize with them; try to do your best in helping them in the time of need and difficulty. (I further advise you to) be patient with the unwise and wrong doers, gain deep understanding of religion, seek education in behavior, show respect to the Holy Qur'an, retain your good nature, advise (others) to good and prevent them from the evils. As Allah states in the Holy Qur'an:

“There is no good in most of their secret counsels except (in his) who enjoins charity or goodness or reconciliation between people; and whoever does this seeking Allah's pleasure, We will soon give him a mighty reward.”2

… Thus, act according to my advice, and ask my followers to do the same. Upon you be waiting for relief, for Prophet Muhammad (S.A.W.) said: “The best of deed in my community is waiting for the relief (the appearance of Imam Mahdi (A.S.)).” Our followers will be in a constant grief until he reappears. He is the one promised by Prophet Muhammad (S.A.W.) who will fill the earth with justice when it has been filled with tyranny and oppression. O my follower! Be patient (for the appearance) and ask all of my followers to endure as well; nevertheless:

“…surely the earth is Allah's; He causes such of His servants to inherit it as He pleases; and the end is for the righteous.”3

May Allah’s mercy and blessing be upon you and all of my followers.

[Narrated from “Guidance to the Path of Light, The Life of Imam Hasan Askari (A.S.)” by Ayatollah Sayyed Muhammad Taqi Mudarresi; translated by Muhammad Sadiq Sharee’at[)

Footnotes:
1- Ali Ibn Babeweyh Qummi, the father of Sheikh Saduq.
2- The Holy Qur'an, 4:114.
3- The Holy Qur'an, 7:128