Jami` at-Tirmidhi Book 18, Hadith 3
"And he was asked about the Mir'ad."
"I said: 'O Messenger of Allah! We send our trained dogs to catch game for us.' He said: 'Eat what it catches for you.' I said: 'O Messenger of Allah, and if they kill it?' He said: 'Even if they kill it, as long as they are not accompanied by some other dogs besides them.'" He said: "I said: 'O Messenger of Allah! We hunt with the Mir'ad.' He said: 'Eat of the game what the Mir'ad pierces, but whatever is struck by its broad side, then do not eat it.'"
"We have been forbidden from the game caught by a Zoroastrian's dog."