From quite early on the Shi?a endeavoured to provide historical and rational arguments for their central claim that ?Al?, the cousin and son-in-law of the Prophet Mu?ammad, was not only his legitimate successor, but also the person best qualified to lead the umma. In particular, there are several statements attributed to the Prophet Mu?ammad which are used as evidence of the special position of ?Al? and his family. One of these is a report known as the ‘?ad?th manzilat H?r?n (?ad?th on the position of Aaron)’ in the Muslim tradition. According to this report, cited by such authorities of ?ad?th as Muslim, al-Tirmidh? and Ibn ?anbal, Mu?ammad said to ?Al?: “Are you not content to be with respect to me as Aaron was to Moses, except that after me there shall be no other Prophet.” It seems this report alludes to the parallels and similarities between the status of Mu?ammad and ?Al? and their close relationship, and that of Moses and Aaron in the Biblical tradition. This paper examines the significance of this report in the formulation of the doctrine of the special status of ?Al? in Sh??? Islam through its use and interpretation in the Muslim literary and historical tradition. The authenticity of the report is not relevant to the discussion here, since the main concern will be to examine the reasons behind this allusion to Moses and Aaron in the Muslim context and the way in which it has been interpreted in the wider debate on authority and theology. In sum, this paper is an attempt to examine how this report has been used to respond to the concerns in the Muslim tradition about such important issues as the concept of prophethood, the position of Mu?ammad as the last prophet, and the question of religious authority.