Sayyidah Umm al-Husayn (may Allah be pleased with her) said: I heard the Prophet (peace and blessings be upon him) while he (peace and blessings be upon him) was wrapped in his cloak, and he was saying: "If a mutilated Abyssinian slave is appointed as your ruler, then listen to him, so long as he establishes among you the Book of Allah Almighty."
Hadith Referenceالمعجم الكبير للطبراني / مسند النساء / 21844