Musnad Ahmad 30:2141

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