Musnad Ahmad 30:2329

Harun ibn Ma'ruf narrated to us, Ibn Wahb narrated to us, he said: Makhramah ibn Bukayr narrated to me, from his father, from 'Arak ibn Malik, he said: I heard Abu Hurayrah narrating from the Messenger of Allah, may Allah bless him and grant him peace, that he said: "There is no charity upon the slave, except for the charity of al-Fitr."