Musnad Abu Ya'la al-Mawsili 110:189

Daud ibn 'Amr narrated to us, Muhammad ibn Muslim narrated to us, from 'Amr ibn Dinar, from 'Ikrimah, from Ibn 'Abbas, that a man said: "O Messenger of Allah, my mother has passed away and she did not leave a will. Will it benefit her if I give charity on her behalf?" He said: "Yes."