Musnad Ahmad 30:406

'Abd al-Wahid narrated to us, from 'Awf, from Khilas, from Abu Hurayrah, that 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 eats until, when it is full, it vomits, then it returns to its vomit and eats it."