Sahih Muslim Book 13, Hadith Number 4001.
Chapter : The deceased is entitled to reward for the sadaqa given after his death.
Abu Huraira (Allah be pleased with him) reported that a person said to Allah’s Apostle (may peace be upon him): My father died and left behind property without making any will regarding it. Would he be relieved of the burden of his sing if I give sadaqa on his behalf? He (the Holy Prophet) said: Yea.