بيعة إبراهيم بن المهدي

In late 201 AH the people were called to give the oath of the caliphate to Ibrahim ibn al-Mahdi. The people of Baghdad gave him the oath in Muharram 202 AH and deposed al-Ma'mun. ^{1 2}

The sources place the call to the oath on page 555, and the oath itself and the deposing of al-Ma'mun on page 557. For this reason the event is recorded under the year 202 AH, with the note that the call preceded it by about a month.