"My mother has died and she had a vow to fulfill. Will it suffice if I free a slave on her behalf?" He said: "Free a slave on behalf of your mother."
Sunan an-Nasa'i Book 30, Hadith 46
← Previous Hadith "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."

Sunan an-Nasa'i Book 30, Hadith 45 Next Hadith → "Fulfill it on her behalf."

Sunan an-Nasa'i Book 30, Hadith 47