Musnad Ahmad 1153:242

Yahya narrated to us, he said: Hisham informed us, he said: My father informed me, he said: Aisha informed me, that a man said to the Prophet, peace and blessings of Allah be upon him: "My mother died suddenly, and I think that if she had been able to speak, she would have given charity. So, does she have a reward if I give charity on her behalf?" He said: "Yes."