Sa'd bin 'Ubadah came to the Prophet and said: "My mother has died and she had a vow to fulfill but she did not do so." He said: "Fulfill it on her behalf."
Sunan an-Nasa'i Book 30, Hadith 53
← Previous Hadith "Sa'd bin 'Ubadah Al-Ansari consulted the Messenger of Allah about an (outstanding) vow that his mother had to fulfill, but she died before doing so. The Messenger of Allah said: 'Fulfill it on her behalf.'"

Sunan an-Nasa'i Book 30, Hadith 52 Next Hadith → "I said: 'O Messenger of Allah, my mother has died; shall I give in charity on her behalf?' He said: 'Yes.' I said: 'What kind of charity is best?' He said: 'Providing drinking water.'"

Sunan an-Nasa'i Book 30, Hadith 54