Umm Husayn Ahmasiyyah (may Allah be pleased with her) says: I heard the Messenger of Allah (peace and blessings of Allah be upon him) delivering a sermon during the Farewell Pilgrimage. He was wearing a cloak wrapped under his armpit, and (as if I am) seeing the flesh of his arm trembling. I heard him say: "O people! Fear Allah, and even if a slave with a cut ear from among the Abyssinians is appointed as your ruler, listen to him and obey him, as long as he establishes the Book of Allah for you" (i.e., as long as he rules according to the Book of Allah) __QUR_N__.

Imam Tirmidhi says:
1- This hadith is Hasan Sahih.
2- (This hadith) is also narrated from Umm Husayn through other chains.
3- In this chapter, ahadith have also been narrated from Abu Hurairah and Irbad bin Sariyah (may Allah be pleased with them) __XREF_N__ __REF_N__.