The Book of Oaths and Vows
35/35. Chapter:
If A Person Dies With A Vow Unfulfilled
Sunan an-Nasai
أَخْبَرَنَا قُتَيْبَةُ، قَالَ حَدَّثَنَا اللَّيْثُ، عَنِ ابْنِ شِهَابٍ، عَنْ عُبَيْدِ اللَّهِ بْنِ عَبْدِ اللَّهِ، عَنِ ابْنِ عَبَّاسٍ، قَالَ اسْتَفْتَى سَعْدُ بْنُ عُبَادَةَ رَسُولَ اللَّهِ صلى الله عليه وسلم فِي نَذْرٍ كَانَ عَلَى أُمِّهِ فَتُوُفِّيَتْ قَبْلَ أَنْ تَقْضِيَهُ فَقَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم " اقْضِهِ عَنْهَا " .
It was narrated that Ibn 'Abbas said: "Sa'd bin 'Ubadah asked the Messenger of Allah about a vow which his mother had sworn, but she died before she could fulfill it. The Messenger of Allah said: 'Fulfill it on her behalf.'"
Reference : Sunan an-Nasa'i 3818In-book reference : Book 35, Hadith 58English translation : Vol. 4, Book 35, Hadith 3849