Musnad Ahmad 25:1410

Al-Walid ibn Muslim narrated to us, Al-Awza'i narrated to us, Abu Ja'far Muhammad ibn Ali narrated to me, that he heard Sa'id ibn al-Musayyib informing that he heard Ibn Abbas saying: The Messenger of Allah, peace and blessings of Allah be upon him, said: "The likeness of the one who gives charity, then returns to his charity, is the likeness of the dog that vomits, then eats its vomit."