(30) باب مَنْ مَاتَ وَعَلَيْهِ نَذْرٌ
Narrated Sa`id bin 'Ubada Al-Ansari:
that he consulted the Prophet (ﷺ) about a vow that had been made by his mother who died without fulfilling it. The Prophet (ﷺ) gave his verdict that he should fulfill it on her behalf. The verdict became Sunna (i.e. the Prophet's tradition).
Reference: Sahih al-Bukhari 6698
In-book reference: Book 83, Hadith 75
USC-MSA web (English) reference(deprecated numbering scheme): Vol. 8, Book 78, Hadith 689