Hadith 948
'Aishah (May Allah be pleased with her) reported:
وعن عائشة رضي الله عنها أن رجلاً قال للنبي صلى الله عليه وسلم : إن أمي افتلتت نفسها وأراها لو تكلمت، تصدقت، فهل لها أجر إن تصدقت عنها؟ قال: "نعم" ((متفق عليه))
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].
In plain words
A man asked whether charity given on behalf of his mother who had died suddenly would benefit her, and the Prophet answered yes, so good deeds done for the deceased still reach them.
Reference : Riyad as-Salihin 948 In-book reference : Book 6, Hadith 55