Sunan an Nasai
3655
Sahih+2

It was narrated from Ibn 'Abbas that a man said:"O Messenger of Allah, my mother died; will it benefit her if I give in charity on her behalf?" He said: "Yes." He said: "I have a garden and I ask you to bear witness that I am giving it in charity on her behalf

SahihAbu Ghuddah
SahihAl-Albani