Sayyiduna Anas bin Malik (may Allah be pleased with him) says that a man from Banu Kilab asked the Messenger of Allah (peace and blessings be upon him) about the mating of a stud animal, and he forbade him from it. He said: O Messenger of Allah! We lend out our stud for mating and we are given a gift in return. So he permitted the gift.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب البيوع / 10853