Musta'li Ismailism

In contrast, the Nizari—the other living branch of Ismailism, presently led by Aga Khan V—believe the ninth caliph was al-Musta'li's elder brother, Nizar.

Historically, there was a distinction between the Tayyibi and the Hafizi Musta'lis, the former recognizing at-Tayyib Abu'l-Qasim as the legitimate heir of the Imamate after al-Amir bi-Ahkam Allah and the latter following al-Hafiz, who was enthroned as caliph.

According to Musta'lī tradition, after the death of al-Amir bi-Ahkam Allah, his infant son, At-Tayyib Abu'l-Qasim, about two years old, was protected by Arwa al-Sulayhi who died in 1138, wife of the chief Fatimid Da'i of Yemen.

She had been promoted to the post of Hujjat al-Islam long before by al-Mustansir Billah when her husband died and ran the Fatimid dawah from Yemen in the name of Imam At-Tayyib Abu'l-Qasim.

According to Fatimid tradition, after the death of Al-Amir bi-Ahkami'l-Lah, Arwa al-Sulayhi instituted the Da'i al-Mutlaq in place of Dai to run the independent dawah from Yemen in the name of Imam Taiyab.

As a small Shi'i group ruling over a majority Sunni population with a Christian minority also, the Fatimid caliphs were careful to respect the sentiments of people.

[6] Al-Aziz Billah rebuilt the Saint Mercurius Church in Coptic Cairo near Fustat and encouraged public theological debate between the chief Fatimid qadi and the bishops of Oriental Orthodoxy in the interest of ecumenism.