Sayyidah Umm al-Husayn (may Allah be pleased with her) said: I performed the Farewell Hajj with the Messenger of Allah (peace and blessings be upon him), and I saw Bilal and Usamah (may Allah be pleased with them both). Bilal (may Allah be pleased with him) was holding the halter of his (peace and blessings be upon him) mount, and the other (Usamah, may Allah be pleased with him) was holding up his garment over him (peace and blessings be upon him) to shade him from the heat, until he (peace and blessings be upon him) stoned Jamrat al-Aqabah. Then he (peace and blessings be upon him) departed, having put his garment under his right armpit and over his left shoulder, and I saw beneath the bone of his (peace and blessings be upon him) right shoulder something like a clenched fist. He (peace and blessings be upon him) stopped for the people and said many things, among which was: "If a black Abyssinian slave is appointed as your ruler who leads you according to the Book of Allah, then listen and obey."
Hadith Referenceالمعجم الكبير للطبراني / مسند النساء / 21842