It is narrated from Thawr bin Yazid (may Allah have mercy on him) that the Messenger of Allah (peace and blessings be upon him) said: "The slaughtered animal of a Muslim is lawful, whether he mentioned the name of Allah when slaughtering or not, for whether he mentions the name of Allah or not, he takes only the name of Allah."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصيد والذبائح / 18895