Sa'd b. 'Ubadah asked the Messenger of Allah (ﷺ): My Mother has died and she could not fulfill her vow which she had taken. The Messenger of Allah (ﷺ) said: Fulfill it on her behalf.
Sunan Abi Dawud Book 22, Hadith 66
← Previous Hadith "The Prophet (ﷺ) said: By Him Who sent Muhammad with truth, if you prayed here, this would be sufficient for you like the prayer in Jerusalem."

Abu Dawud said: This tradition has also been transmitted by al-Ansari, from Ibn-Juraij. He said: Ja'far b. 'Umar and 'Amr b. Hayyah. He said: They transmitted from 'Abd al-Rahman b. 'Awf and from the Companions of the Prophet (ﷺ).

Sunan Abi Dawud Book 22, Hadith 65 Next Hadith → A woman made a voyage and vowed that she would fast one month if Allah made her reach her destination with peace and security. Allah made her reach her destination with security but she died before she could fast. Her daughter or sister (the narrator doubted) came to the Messenger of Allah (ﷺ). So he commanded to fast on her behalf.

Sunan Abi Dawud Book 22, Hadith 67