From Sahih Muslim (Hadith 4221):
A'isha (Allah be pleased with her) reported that a man came to Allah's Apostle (ﷺ) and said:Allah's Messenger, my mother died all of a sudden without making any will. I think if (she could have the opportunity) to speak she would have made a Sadaqa. Would there be any reward for her if I give charity on her behalf? He (the Holy Prophet) said: Yes
Reference: Muslim 4221