The Mahdī is the Fifth of the Descendants of the Seventh (Mūsā al-Kāẓim عليه السلام) & its Particulars

Saʿd b. ʿAbd Allāh, from al-Ḥasan b. ʿAlī al-Zaytūnī, and Muḥammad b. Aḥmad b. Abī Qutāda, from Aḥmad b. Hilāl, from Umayya b. ʿAlī, from Abī’l-Haytham b. Abī Ḥayya, from Abī ʿAbd Allāh عليه السلام, who said: “When three names come together in a sequence: Muḥammad, ʿAlī, and al-Ḥasan, then the fourth is the Qāʾim.”