Sahih Muslim 2326
صحيح مسلم#2326SahihA'isha said that a person came to the Messenger of Allah (ﷺ) and said:My mother died suddenly without having made any will. I think she would have definitely given Sadaqa if she had been able to speak. Would she have a reward if I gave Sadaqa on her behalf? He (the Holy Prophet) said: Yes
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Every narration in Sahih Muslim is accepted as Sahih (authentic) by the established status of the book.
In-book reference: 12:63