Maliks Muwatta Book 24, Hadith Number 1.
Section : Saying the Name of Allah over the Slaughtered Animal.
Yahya related to me from Malik from Hisham ibn Urwa that his father said, “The Messenger of Allah, may Allah bless him and grant him peace, was asked, ‘Messenger of Allah! Some people from the desert bring us meat, and we do not know whether the name of Allah has been mentioned over it or not.’ The Messenger of Allah, may Allah bless him and grant him peace, said, ‘Mention the name of Allah over it and eat.'”
Malik said, “That was in the beginning of Islam.”