When food was brought to the Prophet (peace and blessings be upon him), he (peace and blessings be upon him) would ask: "Is it sadaqah or a gift?" If it was a gift, he would stretch out his hand and take it, and if it was sadaqah, he would say to the Companions (may Allah be pleased with them): "Eat."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب النكاح / 13276