Sahih Muslim Book 021, Hadith Number 4734.
Chapter : Hunting with the help of trained dogs.
'Adi b. Hatim reported that he asked the Messenger of Allah (may peace be upon him) about (hunting) with the help of an arrow having a stub end. He said: If it strikes (the game) with its point, then eat, but if it strikes flatly and it dies, that is Waqidh (beaten into death), do not eat that. I asked the Messenger of Allah (may peace be upon him) about (hunting with the help of) dogs, whereupon he said. When you send your dog (for hunting) reciting the name of Allah, then eat (the game), but if some part of it is eaten (by the dogs, then do not eat that, for it (your dog) has caught that (the-game) for itself. I (again) said: If I find along with my dog another dog, and do not know which of (the dogs) has caught (the game), then (what should I do)? Thereupon he ('Allah's Messenger) said: Then don't eat that, for you recited the name of Allah on your dog and not on the other one.