Musannaf Ibn Abi Shayba 36:356

Abu Dawud narrated to us, from Shu'bah, from Humayd ibn Hilal, from Abdullah ibn Mughaffal, who said: I heard him saying: A leather bag of fat was lowered on the day of Khaybar. He said: So I embraced it and said, "I will not give anyone anything from this." He said: Then I turned around, and behold, the Prophet, peace and blessings of Allah be upon him, was smiling, so I felt ashamed.