Sahih Muslim
The Book of Zakat (Kitab Al-Zakat)
Book Number: 005 / Hadith Number: 2357
Abu Huraira reported: Whenever the Apostle of Allah (may peace be upon him) was presented with food, he asked about it, If he was told that it was a gift, he ate out of that, and if he was told that it was a sadaqa he did not eat out of that.