Saad asked the Messenger of Allah ﷺ for a ruling regarding a vow his mother had taken which she died before fulfilling. The Messenger of Allah ﷺ said, "Fulfill it on her behalf."
أخبرنا العباس بن الوليد بن مزيد قال أخبرني أبي قال حدثنا الأوزاعي قال أخبرني الزهري أن عبيد الله بن عبد الله أخبره
قال استفتى سعد رسول الله ﷺ في نذر كان على أمه فتوفيت قبل أن تقضيه فقال رسول الله ﷺ اقضه عنها
Bukhari narrated it in the Book of Wills, chapter "It Is Recommended for One Whose Relative Died Suddenly to Give Charity on His Behalf... etc.," no. 2761, and Muslim in the Book of Vows, chapter "The Command to Fulfill a Vow," no. 1638, from the hadith of Zuhri through this same chain, and it is also in Kubra, no. 6486.