Sahih Muslim Book 12, Hadith Number 3960.

Chapter : Disapproval of buying the donated property by the donor himself.

Abdullah b. Tawus reported on the authority of his father who reported from Ibn Abas(Allah be pleased with them) who reported from Allah’s Messenger ‘may peace be upon him) that he said: One who gets back his gift is like a dog which vomits and then swallows that vomit.