Sahih Muslim
The Book of Faith (Kitab Al-Iman)
Book Number: 001 / Hadith Number: 431
The same hadith has been narrated from A'mash on the authority of the same chain of transmitters with the exception of these words: You would be no more among men (on the Day of Resurrection) but like a white hair on (the body of) a black ox, or like a black hair on (the body of) a white ox, and he made no mention of: a strip on the foreleg of an ass.