Then, in 306 AH they marched on Egypt together with al-Qāʾim; he took Alexandria and a large part of Upper Egypt.
Later,(1) he withdrew, but they came back in 308 AH and occupied Giza.

As for the Mahdī’s lineage, a variety of views exist, but the sum of them is that he was neither Hāshimite nor descended from Fāṭimah.

He died midway through Rabīʿ al-Awwal 322 AH, at the age of sixty-two.
His reign lasted twenty-five years and some months.(2)

After him his son al-Qāʾim assumed power.

Qāḍī ʿIyāḍ reports in the biography of Abū Muḥammad al-Kastrātī(3) that the latter was asked about someone whom the Banū ʿUbayd forced to embrace their cause on pain of death. He answered, “He must choose death; no dispensation is granted. Flight is obligatory, for it is impermissible to remain in a place where its people are required to suspend the divine law.”(4)

Qāḍī ʿIyāḍ adds: “The scholars of Kairouan unanimously agreed that the condition of the Banū ʿUbayd is the condition of apostates and heretics.”(5)

It is also said that when ʿUbayd Allāh seized the Maghrib he revealed this creed only to his inner circle; once firmly established he intensified the killings, carried off women as captives, and set his sights on taking Egypt.