Najm ad-Din Yahya bin Muhsin was a seventh-generation descendant of imam al-Mukhtar al-Qasim (d. 956). The old imam al-Mansur Abdallah died in 1217 in Kawkaban after many years of inconclusive struggles against the Ayyubids, who established a sub-branch in Yemen in 1173. After the demise of al-Mansur, the loyalties of the Zaidi community were split. People in the traditional centre of the Zaidi polity, Sa'dah, accepted Najm ad-Din Yahya as imam under the name al-Hadi Yahya. However, in the southern parts of the Zaidi land, the old imam's son Izz ad-Din Muhammad was set up as an-Nasir Muhammad. The latter died from a battle wound in 1226. Ayyubid rule in Yemen was replaced in 1229 by the Rasulid Dynasty (1229-1254). The first Rasulid Sultan, Nur ad-Din Umar I, seized several places in the highland, such as San'a, Ta'izz and Kawkaban. In 1231 he concluded peace with the Zaidi community, and there were relatively few Zaidi-Rasulid clashes until 1248. Al-Hadi Yahya died in 1239 and was buried in Saqayn. His death was followed by an interregnum of nine years until al-Mahdi Ahmad bin al-Husayn, from another branch of the Rassids, was proclaimed.
- The descent line is: al-Mukhtar al-Qasim - Muhammad - Abdallah - an-Nasir - Yahya - Yahya - Muhsin - al-Hadi Yahya.
- H.C. Kay, Yaman; Its Early Medieval History. London 1892, p. 319.
- Enzyklopädie des Islam, Vol. III. Leiden 1936, p. 1218.