Musnad Ahmad 9:20

'Ali ibn 'Asim narrated to us, Husayn said: Hilal ibn Yasaf informed us, from 'Abdullah ibn Zalim al-Mazini, who said: When Mu'awiyah left Kufa, he appointed al-Mughirah ibn Shu'bah. He said: So he set up speakers who would disparage 'Ali. He said: I was beside Sa'id ibn Zayd ibn 'Amr ibn Nufayl. He said: He became angry, stood up, and took my hand, so I followed him. He said: "Do you not see this man who is unjust to himself, who commands the cursing of a man from the people of Paradise?" "I bear witness regarding nine that they are in Paradise, and if I were to bear witness regarding the tenth, I would not be sinful." I said: "And how is that?" He said: The Messenger of Allah (ﷺ) said: "Be firm, Hira', for there is upon you nothing but a Prophet, or a Siddiq (truthful one), or a martyr." He said: I said: "Who are they?" He said: The Messenger of Allah (ﷺ), Abu Bakr, 'Umar, 'Uthman, 'Ali, al-Zubayr, Talhah, 'Abd al-Rahman ibn 'Awf, and Sa'd ibn Malik. He said: Then he fell silent. He said: I said: "And who is the tenth?" He said: He said: "I."