Abu Dawud Book 11, Hadith Number 2876.
Chapter : On giving sadaqah on behalf of a man who dies without a will.
Narated By Ibn ‘Abbas : A man said: Apostle of Allah, my mother has died; will it benefit her if I give sadaqah on her behalf? He said: Yes. He said: I have a garden, and I call you to witness that I have given it as sadaqah on her behalf.