An early report states that ʿAlī b. Hishām poisoned al-Riḍā. The source for the report, al-Yaʿqūbī, expresses little confidence in it, introducing it with “it is said” (qīl). But he does seem sure that, if al-Riḍā was poisoned, al-Maʾmūn was not responsible. Given the suspicious timing of al-Riḍā's death and the evidence for al-Maʾmūn's innocence, it appears worthwhile to investigate al-Yaʿqūbī's report more closely. Although the report itself cannot be corroborated, it suggests the broader possibility that someone like ʿAlī b. Hishām – that is, one of al-Maʾmūn's abnā’ commanders – took the step of removing al-Riḍā without the caliph's knowledge or consent. To substantiate the plausibility of this suggestion, it will be necessary to look more closely at other reports of the events in Marv and Ṭūs.

There is ample evidence that the abnāʾ in Baghdad opposed the designation of al-Riḍā. Not surprisingly, their comrades in Khurasan shared their dismay. According to al-Jahshiyārī, al-Maʿmūn asked al-Faḍl b. Sahl to justify to the commander Nuʾaym b. Ḥāzim the designation of al-Riḑā as heir apparent.