Sahih Bukhari: Hadith 175

I asked the Prophet (about the hunting dogs) and he replied, "If you let loose (with Allah's name) your tamed dog after a game and it hunts it, you may eat it, but if the dog eats of (that game) then do not eat it because the dog has hunted it for itself." I further said, "Sometimes I send my dog for hunting and find another dog with it. He said, "Do not eat the game for you have mentioned Allah's name only on sending your dog and not the other dog."