Abu Sahl al-Nowbakhti (311 AH) was one of the prominent Shi‘a theologians during the period of the Lesser Occultation. Muhammad ibn Ishaq al-Nadim made a claim regarding Abu Sahl’s belief in the death of the twelfth Imam, examined in this article. Nadim considers Abu Sahl as one of the great Shi‘a scholars and attributes to him a belief that contradicts the common belief of the Twelver Shi‘a that Imam Mahdi is alive. After introducing Abu Sahl as one of the great virtuous Shi‘a scholars who had a group of theologians as his pupils, he writes, “He believed that Muhammad ibn al-Hasan was the Imam, but he died during the Occultation and his son took over the Imamate after him.” The present study criticizes this claim with a critical approach and analysis of the opinions raised about it. By examining issues such as Abu Sahl's high position among the Shi‘a theologians, the rarity of Nadim's opinion, the statements of Western scholars, the extant writings of Abu Sahl, and the silence of other sources regarding this belief, the results show that there are insufficient reasons for accepting that claim. By presenting and analyzing alternative hypotheses (i.e., taqiyyah or “dissimulation”, change of belief, Nadim's error, and addition to the book entitled al-Fihrist), the possibility of Nadim's error or addition is strengthened. The importance of this study lies not only in examining Abu Sahl's personal perspective, but also in preparing the ground for a better understanding of the history of the Shi‘a thought and the formation of Twelver Shi‘a doctrines.