the holy prophet (s.a.w.a.) replied: 'he shall be from this son (and he put his hand on hussein's head) of mine.
the author of «yanabi-ul-muwadda» on page 49 says: in the commentary on nahjul-balagha (most probably he is referring to commentary of ibn-abil hadeed) qazi-ul-quza'at narrates from kafi-ul-kufa' at, abul-qasim ismail-ibn-ebad a tradition where the chain of transmission is linked to ali (a.s.) who mentioned something about Mahdi and then said:
'verily he is from the children of hussein.(44)
the author says: traditions in this regard are «mustafiza» traditions. rather, the consensus amongst we shia imamiah is the same and what is famous among the scholars of our brethren sunnis too is the same. however in some of the rare traditions (very few) we find something which is opposite to this meaning.
among them, abu dawoud in his 'sahih' (vol. 4, pg. 89) narrates from abu ishaaq who said:
ali (may Allah's peace and blessing be upon him) looked at hassan and said: «surely my son is «sayyid» (chief) just as the holy prophet called him by this name. soon a person will emerge from his rear. his name shall be the same as your prophet's name. in creation he will be similar to the prophet but in behaviour he will not be so. he shall fill the earth with justice».
some of sunni 'ulemas' have reckoned Mahdi to be from the children of abu muhammad hassan mujtaba (a.s.).
amongst them, ibn hajar in his 'sawa'eq' on page 99 writes: «abu dawoud in his 'sunan' has narrated a tradition that Mahdi is from the children of hassan and its mystery lies in this that hassan waived his caliphate for the sake of Allah and his affection for his people. thus Allah placed the «qa'em» (who shall emerge at the time of dire strait) amongst his children so that he fills the earth with justice. the traditions which say that he is from the children of hussein are weak.»
the author says: 'as per the prescribed rules in 'usul-e-fiqh' (principles of jurisprudence) relying on the afore-said tradition is not correct for the following reasons: