The bayʿa (or mubāyaʿa ) is a reciprocal pledge made between a Muslim leader and his followers. The prophet Muḥammad is said to have taken bayʿa s from his followers, notably the "second pledge at al-ʿAqaba," where mutual obligations of assistance in war were exchanged with supporters from Yathrib (later Medina). In Sunnī Islam, a bayʿa , made by the (only vaguely defined) "people who loosen and bind" (ahl al-ḥall wa-l-ʿaqd) , is the means by which the caliph is recognised. A bayʿa can also commonly be taken by