Musannaf Ibn Abi Shayba 23:171

Abdullah ibn Idris narrated to us, from Husayn, from Abd al-Rahman ibn Abi Layla, who said: The Messenger of Allah (may Allah bless him and grant him peace) said: "I saw myself being followed by black sheep, followed by dust-colored sheep." Abu Bakr said: "O Messenger of Allah, these are the Arabs following you, followed by the non-Arabs." He said: The Messenger of Allah (may Allah bless him and grant him peace) said: "Thus did the angel interpret it."