(15) بَابُ إِذَا قَالَ أَرْضِي أَوْ بُسْتَانِي صَدَقَةٌ عَنْ أُمِّي. فَهُوَ جَائِزٌ، وَإِنْ لَمْ يُبَيِّنْ لِمَنْ ذَلِكَ
Narrated Ibn `Abbas:
The mother of Sa`d bin 'Ubada died in his absence. He said, "O Allah's Messenger (ﷺ)! My mother died in my absence; will it be of any benefit for her if I give Sadaqa on her behalf?" The Prophet (ﷺ) said, "Yes," Sa`d said, "I make you a witness that I gave my garden called Al Makhraf in charity on her behalf."
Reference: Sahih al-Bukhari 2756
In-book reference: Book 55, Hadith 19
USC-MSA web (English) reference(deprecated numbering scheme): Vol. 4, Book 51, Hadith 19