Musnad Ahmad 600:1

Yazid ibn Harun narrated to us, Muhammad ibn Ishaq informed us, from Yazid ibn Abi Habib, from Marthad ibn Abdullah al-Yazani, that some of the companions of the Messenger of Allah (peace and blessings of Allah be upon him) narrated to him that he heard the Messenger of Allah (peace and blessings of Allah be upon him) say: "Indeed, the shade of the believer on the Day of Resurrection is his charity."