the Isma'ili was split when the Qarmatians renounced the movement's secret leadership in Salamiya, when the future founder of the Fatimid Caliphate, Abdallah al-Mahdi Billah, dropped the notion of the return of Muhammad ibn Isma'il and proclaimed himself as the . Both Ibn Hawshab and Ibn al-Fadl remained loyal to al-Mahdi. Al-Mahdi was soon forced to flee Salamiya, and in 905, when he was in Egypt, he deliberated between moving on to Yemen or the Maghreb. In view of later events, Wilferd Madelung suggests that doubts about Ibn al-Fadl's loyalty may have played a role in his eventual decision to choose the Maghreb. Indeed, the Isma'ili chief Firuz, who at Salamiya had been the chief proxy () for al-Mahdi, abandoned the latter at Egypt and joined Ibn al-Fadl. On 25 January 905, Ibn al-Fadl evicted his erstwhile ally from Mudhaykhira. The two Isma'ili leaders now exploited Yemen's political division to expand their domains: in November 905, Ibn al-Fadl captured Sana'a, which allowed Ibn Hawshab to in turn seize the Yu'firid base of Shibam. With the exception of Zaydi-held Sa'ada in the north, Ziyadid-ruled Zabid on the western coast, and Aden in the south, all of Yemen was now under Isma'ili control. In late 905, for the first time since coming to Yemen 25 years earlier, the two men met at Shibam. Madelung writes that the meeting "was evidently uneasy", as Ibn Hawshab warned Ibn al-Fadl against overextending his forces, which the latter disregarded. Ibn al-Fadl was the most active of the two in the following years, campaigning across the country against those who still opposed the : in spring 906 he subdued the mountain massifs of Hadur and Haraz and conquered the cities of al-Mahjam, al-Kadra, and, briefly, even Zabid. Both Sana'a and Shibam were briefly lost to the Zaydi imam al-Hadi in 906, but Shibam was recovered before the end of the year, and Ibn al-Fadl reoccupied Sana'a on 17 April 907. Sana'a changed hands a few times again over the following years, until it was finally captured by Ibn al-Fadl in August 911. Revolt against Abdallah al-Mahdi Billah At this point, Ibn al-Fadl publicly renounced allegiance to Abdallah al-Mahdi Billah, who had revealed himself and established the Fatimid Caliphate in Ifriqiya in 909. The exact reason for Ibn al-Fadl's denunciation is not known; it may have been personal ambition, following his many successes, or disillusionment with al-Mahdi. Al-Mahdi