Sahih Muslim Book 21, Hadith Number 4739.

Chapter : Hunting with the help of trained dogs.

Sha’bi reported: I heard Adi b. Hatim say-and he was our neighbour, and our partner and co worker at Nahrain-that he asked Allah’s Apostle (may peace he upon him) saying: I let off my dog and find another dog along with my dog and that (any one of them) catches the (game), but I do not know which one had caught it, whereupon he (the Holy Prophet) said: Then don’t eat that, for you recited the name of Allah while letting off your dog and did not recite on the other.