This paper deals with the succession to the prophet Muḥammad. After a sketch of the historical developments connected with the succession of Muḥammad, it discusses an episode that is said to have taken place late in Muḥammad’s career at the pond of Khumm (the so-called Ghadīr Khumm episode). From what Muḥammad said there, Shiites deduce that, indeed, his cousin ʿAlī should have become his successor, while Sunnis, although generally accepting the episode (ḥadīth) as genuine, explain that Muḥammad wanted to stop any critique of ʿAlī, but did not intend to invest him as his successor. This leads to the third part, a discussion of events that took place in the early tenth century CE, when the Shiite Fatimids conquered what today is Tunisia and installed a Shiite caliphate in a Sunni environment. This paper will show how the ḥadīth of Ghadīr Khumm was used in this situation to argue for or against the Shiite claims.