In 1391, when the elderly imām al-Nasir Muhammad Salah al-Din died, his sons were still minors.
Al-Mahdī Aḥmad and his followers withdrew from San'a to Bayt Baws, and for one year the two imāms fought for supremacy.
In 1399, aided by prison guards, the ex-imām escaped to live in privacy until his death from plague in 1436.
[1] Although al-Mahdī Aḥmad lacked the requisite administrative and military skills for the Zaydiyyah imamate, he produced a substantial body of writings on dogmatics, logic, poetry, grammar and law.
The famous Salafi scholar Muhammad Al-Shawkani wrote Al-Sayl al-jarrar, a denunciation of a text written by the Zaydi Imam Al-Mahdi Ahmad bin Yahya.