Musnad Ahmad 25:763

Ahmad ibn Abd al-Malik narrated to us, Musa ibn A'yan narrated to us, 'Amr ibn al-Harith narrated to us, from Bukayr ibn 'Abd Allah, from Sa'id ibn al-Musayyib, who said: I heard Ibn 'Abbas saying: I heard the Messenger of Allah, peace and blessings of Allah be upon him, saying: "The likeness of the one who gives charity, then returns to his charity, is like the one who vomits, then eats his vomit."