to the School of the Caliphate
reports that Abdullah ibn Abbas remarked that the Messenger of Allah (s.a.w.s.)
said, "I am the chief of the Prophets and Ali ibn Abi Talib is the chief
of successors, and after me my successors shall be twelve, the first of
them being Ali ibn Abi Talib and the last of them being Al Mahdi."
Al-Juwayni has also mentioned another tradition from Ibn 'Abbas (r.a.)
that he narrates from the Messenger of Allah (s.a.w.s.):
"Certainly my Caliphs and my legatees and the Proofs of Allah upon
his creatures after me are twelve. The first of them is my brother and
the last of them is my (grand) son."
He was asked: "O Messenger of Allah, who is your brother?"
Al-Juwayni also narrates from his chain of narrators that the Messenger
of Allah (s.a.w.s.) informed:
He said, "Ali ibn Abi Talib"
Then they asked, "And who is your son?"
The Holy Prophet (s.a.w.s.) replied, "Al Mahdi, the one who will fill
the earth with justice and equity like it would be brimming with injustice
and tyranny. And by the One Who has raised me as a warner and a give of
good tidings, even if a day remains for the life of this world, the Almighty
Allah will prolong this day to an extent till he sends my son Mahdi, then
he will make Ruhullah 'Isa ibn Maryam (a.s.) to descend and pray behind
him (Mahdi). And the earth will be illuminated by his radiance. And his
power will reach to the east and the west."
"I and Ali and Hasan and Husayn and nine of the descendants of Husayn
are the purified ones and the infallible." 
Among the scholars of the School of the Caliphate it was the general tendency,
due to the political expediency, to conceal such traditions from the people.
A majority of their scholars have tried their best to explain away these
traditions in a confusing manner. They have endeavoured to make vague guesses
regarding the names of the Caliphs mentioned in these reports. On the other
hand the Holy Prophet (s.a.w.s.) has mentioned clearly, by name, his Twelve
It is not possible to relate all such traditions in this brief treatise.
However we shall present the biographical sketches of the Imams (a.s.)
who have been named by the Messenger of Allah (s.a.w.s.).
||Al-Dhahabi says in Tadhkirat al-Huffaz,
vol. 4, p. 298, that Sadruddin Ibrahim bin Muhammad bin al-Hamawayh al-Juwayni
al-Shafi'i was a great scholar of Hadith. Also see his biographical note
in Ibn Hajar al-'Asqalani, al-Durar al-kaminah, vol. 1, p. 67.
||Al-Juwayni, Fara'id al-Simtayn, pg 160.