Imamate is not Rightfully Invested except In the Descendants of al-Ḥusayn to the Exclusion of the Descendants of al-Ḥasan عليهما السلام

Saʿd, from al-Ḥasan b. Mūsā al-Khashshāb, from ʿAlī b. Ḥassān al-Wāsiṭī, from his paternal uncle, ʿAbd al-Raḥmān b. Kathīr, who stated: “I said to Abī ʿAbd Allāh عليه السلام: What did Allāh تعالى mean by His statement: ﴾Indeed Allāh desires to repel all impurity from you, O’ People of the Household, and purify you with a thorough purification﴿?” [33:33]—He responded: “It was revealed in regard to the Prophet صلى الله عليه وعلى آله, Amīr al-Muʾminīn, al-Ḥasan and al-Ḥusayn (and Fāṭima) عليهم السلام. When Allāh took back (the soul of) His Prophet, it was Amīr al-Muʾminīn (who had authority), then al-Ḥasan, and then al-Ḥusayn عليهم السلام.[1] After that, the interpretation of the verse: ﴾the blood relatives are more entitled to inherit from one another in the Book of Allāh﴿ [33:6] was put into effect, so it was ʿAlī b. al-Ḥusayn عليه السلام (who inherited authority), and then it continued to apply upon the Imams from among his offspring, who are the Legatees. Obedience to them is obedience to Allāh, and disobedience of them is disobedience of Allāh.”