Saad bin Ubada asked the Prophet ﷺ about a vow his mother had made which she had not fulfilled before she died. He said, "Fulfill it on her behalf."
حدثنا سفيان حدثنا الزهري عن عبيد الله
أن سعد بن عبادة سأل النبي ﷺ عن نذر كان على أمه توفيت قبل أن تقضيه فقال اقضه عنها
Its isnad is sahih. Abu Dawud and Nasai also narrated it. He said in al-Muntaqa 4935, "It meets the standard of sahih." See also 1861.