أمير المؤمنين
The conditions set by Hassan ibn Ali are proof of this statement. Sheibani continues: The fact that one of the conditions of peace was that Mu'awiyah do not call himself "Amir al-Mu'minin" is the reason why he did not consider Mu'awiyah worthy of the caliphate; also, when Mu'awiyah invited Hassan to join him in the war with the Kharijites, Hassan did not accept it, which indicates that Hassan ibn Ali did not recognize Mu'awiyah's caliphate.