Hadith 548
Sayyiduna Anas (may Allah be pleased with him) reports: A man from Banu Kilab came to the Messenger of Allah (peace and blessings be upon him) and asked him about the earnings from a bull (stud fees). The Prophet (peace and blessings be upon him) forbade him from it. He said: O Messenger of Allah! We leave it (the bull) with the female (for mating) and we receive a gift for it without any condition. So the Prophet (peace and blessings be upon him) permitted him.