Following the death of Mutawwakil's heir, al-Muntasir, a few months later, Bugha and the other Turkic commanders of the Abbasid army selected al-Musta'in as his successor (see the "Anarchy at Samarra").
Mustafa Ben Halim, "Safahat Matwiya men Tarikh Libia as Siyasi", Matabe' al-Ahram at Tejariya, Qalyub, Misr, 1992.