Musnad Ahmad 30:2249

'Affan narrated to us, Qasim ibn al-Fadl narrated to us, my father narrated to me, from a man from Mahrah, who said: Abu Hurairah said: "O Mahri, the Messenger of Allah (may Allah bless him and grant him peace) forbade the price of a dog, the earnings of a prostitute, the earnings of a cupper, and the earnings of the stud of a stallion."