Al-Hajjaj asked him...
And Zakariyya, Yahya, `Isa and Ilyas were Guided. They were all of Allah’s virtuous creatures. (6:84-85)” After reciting this verse, al-Shi`bi said that `Isa -Jesus- (a.s) too has been included in the Progeny of Ibrahim (a.s) definitely because he descended Ibrahim (a.s) through his mother Maryam.
When we treat `Isa (a.s) as the progeny of Ibrahim (a.s) through his mother Maryam bint `Imran, then why Imam al-Hasan and Imam al-Husayn (a.s) cannot be termed the progeny of Muhammad (a.s) through his daughter Fatimah al-Zahra’, their mother! In the case of `Isa (a.s) there was a difference of several generations between his ancestor, Ibrahim (a.s) and himself. But in the case of Imam al-Hasan and Imam al-Husayn (a.s), they were the next of kin to the Prophet (a.s)!
Hearing this al-Hajjaj kept quiet. Once `Amr ibn al-`As criticized `Ali (a.s) for calling Imam al-Hasan and Imam al-Husayn (a.s) as the sons of the Prophet (a.s). When the Imam (a.s) heard this he asked the informer to tell the enemy of Allah (`Amr) that if they are not his sons, then the Prophet (a.s) would be termed abtar (issueless) as his father al-`As ibn Wa’il used to call the Prophet (a.s). The truth is that Allah has termed the enemies of the Prophet (a.s) abtar instead of him!
Mu`awiyah’s slave Dhakwan says that once Mu`awiyah said that instead of calling Hasan and Husayn (a.s) as the sons of the Prophet (a.s) they should be called the sons of `Ali (a.s) because they are not from the backbone of the Prophet (a.s). Dhakwan says further that Mu`awiyah instructed him to prepare a list of his progeny. He prepared a roster of his sons and the grand children and presented to his master.
Mu`awiyah asked him why he did not add the names of his grand children through his daughters.