Sunan Ibn Majah, Chapter: The Chapters on Marriage

a man from the desert people came to the Prophet (saw) and said: "O Messenger of Allah (saw), my wife has given birth on my bed to a black boy, and there are no black people among my family." He said: "Do you have camels?" He said: "Yes." He said: "What colour are they?" He said: "Red." He said: are there any black ones among them?" He said, "No." He said: "Are there any grey ones among them?" He said "Yes." He said "How is that?" He said: "Perhaps it is hereditary." He said: "Perhaps (the colour of) this son of yours is also hereditary."