The Mahdī is of the Descendants of al-Ḥusayn عليه السلام

Saʿd b. ʿAbd Allāh said: “Yaʿqūb b. Yazīd narrated to us, from Ḥammād b. ʿĪsā from ʿAbd Allāh b. Muskān, from Abān b. Taghlib, from Sulaym b. Qays al-Hilālī, from Salmān al-Fārisī رضي الله عنه, who narrated: “I entered upon the Prophet صلى الله عليه وعلى آله وسلم while al-Ḥusayn was on his lap and he was kissing al-Ḥusayn’s eyes and mouth, saying: “You are a master and the son of a master, and you are an Imam and the son of an Imam, and the father of the Imams. You are the Divine authority of Allāh and the son of His Divine authority, and the father of nine Divine authorities originating from your loins, the ninth of whom is their Qāʾim.”