Sahih Muslim
Sahih Muslim Book 012, Hadith Number 3957.
Hadith Section/Book: Sahih Muslim Sahih Muslim Book 12. Gifts
Chapter : Disapproval of buying the donated property by the donor himself.
Ibn Abbas (Allah be pleased with them) reported: I heard Allah's Messenger (may peace be upon him) say: The similitude of one who gives a charity and then gets it back is like that of a dog which vomits and then eats its vomit.