Ibn al-Fadl's conversion opened the prospect of extending the secret Isma'ili missionary mission () to Yemen. For this purpose, Ibn al-Fadl teamed up with an older convert, the
Kufan
Ibn Hawshab. Setting off in late May or early June 881, the two men made for Kufa, where they joined the pilgrim caravans, whose multitudes, gathered from all corners of the Islamic world, allowed them to travel with anonymity. After completing the rituals of the pilgrimage at Mecca, the two men arrived in northern Yemen in August. Yemen was at the time a troubled province of the
Abbasid empire. Caliphal authority had traditionally been weak and mostly limited to the capital,
Sana'a, while in the rest of the country, tribal conflicts, sometimes dating to pre-Islamic times, persisted. At the time of Ibn al-Fadl and Ibn Hawshab's arrival, the government was politically fragmented and only loosely under the control of Abbasid suzerainty. Much of the interior was held by the
Yu'firid dynasty, who as
Sunnis, recognized the Abbasids. After capturing Sana'a in 861, their rule extended from
Sa'ada in the north to (northeast of
Taiz) in the south and
Hadramawt in the east. A rival dynasty, the
Ziyadids, also nominally loyal to the Abbasids, held
Zabid on the western coastal plain, and at times exercised significant control over wide portions of the country. The
Banu Manakh family ruled the
southern highlands around Taiz, while the
northern parts of the country were in practice dominated by warring tribes owing allegiance to no-one. The lack of political unity, the remoteness of the province and its inaccessible terrain, along with deep-rooted Shi'a sympathies in the local population, made Yemen "manifestly fertile territory for any charismatic leader equipped with tenacity and political acumen to realise his ambitions". After travelling through Sana'a and al-Janad, Ibn Hawshab stayed for a while in
Aden. At some point, then or earlier, Ibn al-Fadl left his colleague, and returned to his home region, where he began proselytizing independently in the mountains of Jebel Yafi'i. From this base in the mountains, he began spreading his message in the surrounding areas. He soon secured the support of the ruler of
Mudhaykhira. With his help, Ibn al-Fadl led successful attacks against the Emir of Lahj, who controlled the highlands north of Aden. At the same time Ibn Hawshab created another Isma'ili stronghold to the north of the country, in the mountains northwest of Sana'a. Both men propagated the belief in the imminent coming of the . While the two Isma'ili s expanded their influence, in 897, another Shi'a leader entered Yemen:
al-Hadi ila'l-Haqq Yahya, a representative of the rival
Zaydi sect, established a state based in Sa'ada, with himself as
imam. In the original Isma'ili doctrine, the expected was
Muhammad ibn Isma'il. However, in 899, the Isma'ili was split when the Qarmatians renounced the movement's secret leadership in Salamiya, following the future founder of the
Fatimid Caliphate,
Abdallah al-Mahdi Billah, who dropped the notion of the return of Muhammad ibn Isma'il and proclaimed himself 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==