Mohtashim Kashani had a son, who died young, so he composed a few couplets in his grief. One night, he saw the Messenger of Allah (s) in dream, who said: You have composed a an elegy (Marsiya) for your son, but did not compose one for my son?
Mohtashim says: I woke up; but since I had never done that before, I did not know how to begin a Marsiya for Imam Husayn.
The following night again I saw the Holy Prophet (s) in dream and he was asking me: Why do you not compose a Marsiya about the tragedy of my son?
I said humbly: Because I have never done this before.
The Holy Prophet (sawa) said, Say – Now, what is the revolution, which has taken place among the creatures of the world?
I woke up and took this to be the opening line of my Marsiya and added the rhyming lines to it. Till I reached the following line: It is in grief, even though it may be the being of the Mighty and Sublime.
But at this point I encountered a block and did not know how to conclude; lest it may be audacity against Almighty Allah.
At night I saw the Imam of the Time, Imam Mahdi (as) in my dream and he asked, Why don’t you conclude your Marsiya?
I said: I could not proceed beyond this line.
The Imam (as) said, Say: He is in the heart and there is no heart without grief.
I woke up and adding this line, concluded my verse.
Today these verses are used in places of mourning as a reminder of this incident.
(Al-Kalaam Yajirul Kalaam volume 2 page 110)