It is narrated from Sayyiduna al-Bara' bin Azib (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) forbade the price of a dog, the earnings of a prostitute, the earnings of the cupper, the fee of the soothsayer, and the fee for a stud animal's mating. And al-Bara' (may Allah be pleased with him) had a billy goat; whoever wanted it to mate (with his she-goat), he would not refuse him, and he would not take any fee for it.
Hadith Referenceالمعجم الكبير للطبراني / باب الباء / 1165