Saad bin Ubada al-Ansari sought a ruling from the Prophet ﷺ regarding a vow his mother had taken which she had not fulfilled before her death. The Prophet ﷺ instructed him to fulfill it on her behalf, and this became the established practice thereafter.
أن سعد بن عبادة الأنصاري استفتى النبي ﷺ في نذر كان على أمه، فتوفيت قبل أن تقضيه، فأفتاه أن يقضيه عنها، فكانت سنة بعد.
Bukhari narrated it in the Book of Oaths and Vows (6698), from Abu Yaman, who said, Shuayb told us, from Ibn Shihab Zuhri, from Ubaydullah bin Abdullah, from Ibn Abbas, and he related it.Muslim narrated it in the Book of Vows (1638-1) through the route of Layth, from Zuhri with his chain, but he did not mention in it, "and this became a practice afterward." Muslim likewise narrated it from a group of narrators who transmitted from Zuhri, other than Shuayb, from Zuhri.Bukhari alone narrated, through Shuayb from Zuhri, the addition "and this became a practice afterward."Ibn Hajar said, "This makes the heir's discharge of what was owed by the deceased a legal method more general than being either obligatory or merely recommended. I have not seen this addition except in the narration of Shuayb from Zuhri." He then mentioned others who narrated from Zuhri and did not mention this addition. He then said, "I think it is from the words of Zuhri himself, though it is possible it came from his teacher. This addition contains a rebuttal of what has been reported from Malik, that no one should perform hajj on behalf of another. He argued that no report had reached him, from anyone among the people of the Abode of Migration since the time of the Messenger of Allah, that anyone had performed hajj on behalf of another, nor had he been commanded to do so, nor permitted to do so."It may be said to those who followed his view, this report did reach others besides him. This Zuhri is counted among the jurists of the people of Madinah, and he was the teacher in this hadith. Ibn Hazm Zahiri, and those who agreed with him, used this addition as evidence that the heir is obligated to discharge the vow on behalf of the deceased in all cases."Fath al-Bari (11/584-585)