Al-Mahdī ʿAbbās b. al-Manṣūr bi-llāh al-Ḥusayn b. al-Qāsim (r. 1161–89/1748–75) was a ruler of the Qāsimī line (1006–1382/1597–1962) of Zaydī Shīʿī Imāms in Yemen. He is considered one of the greatest Imāms of that line by Zaydī scholars, and it is reported that he received an oath of allegiance (bayʿa) from all prominent religious scholars (ʿulamāʾ), as well as from his kinsmen, including those who had refused to accept the “summons” (daʿwa) of his father, Imām al-Manṣūr bi-llāh al-Ḥusayn b. al-Mutawakkil ʿalā llāh al-Qāsim (r. 1139–61/1727–48) (Zabāra, 2:6).

Muḥammad b. ʿAlī al-S…