Eessa bin al-Fat~h was in prison with Imam Abu Muhammad (a.s.). Imam Abu Muhammad (a.s.) said to him, ‘O Eessa, you are sixty-five years and a month and two days old.’
Eessa was astonished. He reviewed his birth date in a book with him and found it was as the imam told.
Then the imam asked Eessa if he had a son and he said he had not.Imam Abu Muhammad (a.s.) prayed Allah for him saying, ‘O Allah, give him a son to be a support for him. The best of support a son is…’
Eessa said, ‘O my master, and you? Do you have a son?’
Imam Abu Muhammad (a.s.) said, ‘By Allah, I shall have a son who will fill the earth with justice and fairness, but not now.’ ( Jawharat al-Kalam, p.155. )