Sayyidah Umm al-Husayn (may Allah be pleased with her) narrates: I saw the Messenger of Allah (peace and blessings be upon him) during the Farewell Hajj. He (peace and blessings be upon him) was admonishing the people and giving them commands, and among what I heard was that he (peace and blessings be upon him) was saying: "If a mutilated Abyssinian slave is appointed as your ruler and he establishes among you the Book of Allah, then listen to him and obey."
Hadith Referenceالمعجم الكبير للطبراني / مسند النساء / 21841