Lady Umm al-Husayn (may Allah be pleased with her) narrated: I saw the Prophet Muhammad (peace be upon him) delivering a sermon in the plain of Arafat. He was saying: "If a mutilated-nosed, Abyssinian slave is appointed as your leader, then listen to him and obey him, as long as he upholds the religion of Allah among you."
Hadith Referenceمسند اسحاق بن راهويه / كتاب الامارة / 888
Hadith Takhrij«مسلم ، كتاب الامارة ، باب وجوب طاعة الامراء فى غير معصية الخ ، رقم : 1837 . سنن ترمذي ، ابواب الجهاد ، باب طاعة الامام ، رقم : 1706 . مسند احمد : 69/4 . 381/5 .»