Musnad Ahmad 30:3251

Muhammad ibn Ja'far narrated to us, he said: 'Awf narrated to us, from Khallas, from Abu Hurayrah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "The likeness of the one who returns to his gift is like the likeness of a dog that ate until, when it was full, it vomited, then it returned to its vomit and ate it."