Al-Ma'mun, in an attempt to win over the Shi'a Muslims to his camp, named the eighth Imam, Ali ar-Rida, his successor, if he should outlive al-Ma'mun. Most Shi'ites realized, however, that ar-Rida was too old to survive him and saw al-Ma'mun's gesture as empty; indeed, al-Ma'mun poisoned Ali ar-Rida who then died in 818. The incident served to further alienate the Shi'ites from the Abbasids, who had already been promised and denied the Caliphate by Abu al-'Abbas.
