Musnad Ahmad 30:1345

Yunus narrated to us, Hammad ibn Salamah narrated to us, from Muhammad ibn Ziyad, who said: I heard Abu Hurairah saying: When food was brought to the Messenger of Allah (peace and blessings of Allah be upon him) from someone other than his family, he would ask about it. If it was said to him, "It is a gift," he would eat. And if it was said, "It is charity," he would say, "Eat," and he would not eat.