Abu Dawud Book 11, Hadith Number 2875.
Chapter : On giving sadaqah on behalf of a man who dies without a will.
Narated By ‘Aisha, Ummul Mu’minin : A woman said: Apostle of Allah, my mother suddenly died; if it had not happened, she would have given sadaqah (charity) and donated (something). Will it suffice if I give sadaqah on her behalf? The Prophet (PBUH) said: Yes, give sadaqah on her behalf.