Musnad Ahmad 30:896

'Abd al-Rahman narrated to us, Hammad ibn Salamah narrated to us, from Muhammad ibn Ziyad, who said: I heard Abu Hurayrah saying: When food was brought to the Prophet, may Allah bless him and grant him peace, from someone other than his family, he would ask about it. If it was said: "It is a gift," he would eat. And if it was said: "It is charity," he would say: "Eat," and he would not eat.