Sahih Bukhari Volume 3, Book 34, Hadith Number 273.

Narated By ‘Aisha : Some people said, “O Allah’s Apostle! Meat is brought to us by some people and we are not sure whether the name of Allah has been mentioned on it or not (at the time of slaughtering the animals).” Allah’s Apostle said (to them), “Mention the name of Allah and eat it.”