Sunan an-Nasa'i 3692

It was narrated that Tawus said:"The Messenger of Allah said: 'It is not permissible for anyone to give a gift then take it back, except from one's son.'" Tawus said: "When I was young I used to hear (the phrase), 'The one who goes back to his vomit,' but we did not realize that this was a similitude." He said: "The likeness of the one who does that is that of a dog which eats then vomits, then goes back to its vomit