ʿAbdullah was succeeded as head of the Ismaʿilian sect by his son Ahmad. According to the _Fihrist_ he was succeeded first by his son Muhammad, then by a second son Ahmad, the latter being also described as the son of Muhammad, and so grandson of ʿAbdullah (_Fihrist_, p. 137). This Ahmad may be the one who was at Basra for some time, then at Kufa, whence in 266 or thereabouts he sent missionaries to Yemen; possibly he was the Ahmad al-Qaiyal who wrote a book on the Imamate, which was refuted by Razi (d. 320). After Ahmad came his son Husayn, who died not long afterwards, leaving a son named Saʿid, who subsequently took the name of ʿUbayd Allah, and was the Mahdi who established the Fatimid State in North Africa, dying in A.H. 323 (= A.D. 934). That he was originally called Saʿid is generally admitted, but he appears variously as Saʿid son of Husayn son of Ahmad, and Saʿid son of Ahmad, and Saʿid son of Abu Shalaghlagh. The explanation given for these different names is that Ahmad had two sons, of whom the elder, Husayn, died whilst Saʿid was still young, and the son was adopted by his uncle Muhammad, the second son of Ahmad, who was also known as Abu Shalaghlagh. There is a story that Saʿid or ʿUbayd Allah was the son of an obscure Jewish smith, whose widow was married to Husayn, son of Ahmad, and that he was adopted by his step-father. This is one of the three forms of what we may call the “Jewish legend,” the attempt to trace the Fatimid dynasty to a Jewish source. These three attempts are: (i.) that Maymun b. Daysan the oculist was a Jew; (ii.) that ʿUbayd Allah was really the son of a Jewish smith; and (iii.) that he was killed in prison at Sijilmassa, and afterwards personated by a Jewish slave. Probably the “Jewish legend” was associated with the fact that the renegade Jew, Ibn Killis, was the one who encouraged the Fatimids to invade Egypt and did most to organise their government there, and with the undoubted favouritism which the early Fatimids showed the Jews. A new development in the teaching of the sect took place under Husayn, or possibly commenced under his father Ahmad. ʿAbdullah had been content to describe himself as the “Mahdi” or guide, who was to lead men to the Imam, who was Ismaʿil, or his son Muhammad; he made no claim to be himself a descendant of the Imam. Probably it was a later theory that the Imam was “concealed” only in the sense that he had to hide himself from the ʿAbbasid Khalif. Later still, when a Fatimid Khalif was actually ruling in Cairo, the claim to descent from ʿAli through ʿAbdullah and his family became a matter of heated controversy.