Riyad us Saliheen: Hadith 947

A man said to the Prophet (ﷺ): "My mother has died suddenly. I think that if she were able to talk (alive) she would have given in Sadaqah (charity). So, if I give Sadaqah now on her behalf, will she get the reward?" The Messenger of Allah (ﷺ) said, "Yes (she will be rewarded for that)."

[Al-Bukhari and Muslim].