the fourth of Shawwāl, and he seized the Caliphal Palace with everything in it, even stripping the Caliph’s wives and favored ladies of their jewels, wrought gold and silver, ceremonial garments, and other valuables. He then convened the judges and jurists, producing for them al-Rāshid’s own written declaration that, should he leave Baghdad to fight the sultan, he was to be considered self-deposed from the caliphate. Some of the jurists thereupon issued fatwas confirming his deposition, and he was deposed on Monday, the sixteenth day of the month (1) [of Dhu al-Qaʿdah, by the ruling of the chief judge and the legal opinion of the senior jurists. His caliphate had lasted eleven months and eleven days. The sultan then] (2) summoned his uncle al-Muqtafi ibn al-Mustazhir, who was invested with the caliphate in place of his brother al-Rāshid bi’Llāh.
[The caliphate of al-Muqtafi li-Amrillāh, Abū ʿAbd Allāh Muḥammad ibn al-Mustazhir bi’Llāh]
His mother was Ṣafrāʾ, called Nasīm (3) and also known as Sitt al-Sādah. He was forty years old at the time. He was proclaimed caliph two days after al-Rāshid’s deposition, and his name was proclaimed from the pulpits on Friday, the twentieth [of Dhu al-Qaʿdah (4)]. He was given the honorific al-Muqtafi because, it is said, he saw the Prophet (5) ﷺ in (6) a dream, and the Prophet said to him: (sayasilu hādhā l-amru ilayka—“This affair will come to you. Follow me.”) Six days later the caliphate did indeed reach him, and for that reason he received the title.

A useful note that merits (7) attention (8):

Both al-Muqtafi and al-Mustarshid acceded to the caliphate, and they were brothers; likewise al-Saffāḥ and al-Manṣūr; al-Hādī and al-Rashīd, the sons of al-Mahdī; and al-Wāthiq and al-Mutawakkil, the sons of al-Muʿtaṣim, were pairs of brothers who each became caliph.

As for three brothers who all held the caliphate: they were al-Amīn, al-Maʾmūn, and al-Muʿtaṣim, the sons of al-Rashīd; and al-Muntaṣir, al-Muʿtazz, and al-Muʿtamad, the sons of al-Mutawakkil.