Sunan an-Nasa'i, Book 35, Hadith 59 (In-Book) ⓘ
It was narrated that Ibn 'Abbas said: "Sa'd bin 'Ubadah came to the Prophet and said: 'My mother died and she had sworn a vow, but she did not fulfill it.' He said: 'Fulfill it on her behalf.'"
أَخْبَرَنَا مُحَمَّدُ بْنُ آدَمَ، وَهَارُونُ بْنُ إِسْحَاقَ الْهَمْدَانِيُّ، عَنْ عَبْدَةَ، عَنْ هِشَامٍ، - وَهُوَ ابْنُ عُرْوَةَ - عَنْ بَكْرِ بْنِ وَائِلٍ، عَنِ الزُّهْرِيِّ، عَنْ عُبَيْدِ اللَّهِ بْنِ عَبْدِ اللَّهِ، عَنِ ابْنِ عَبَّاسٍ، قَالَ جَاءَ سَعْدُ بْنُ عُبَادَةَ إِلَى النَّبِيِّ صلى الله عليه وسلم فَقَالَ إِنَّ أُمِّي مَاتَتْ وَعَلَيْهَا نَذْرٌ فَلَمْ تَقْضِهِ . قَالَ " اقْضِهِ عَنْهَا " .
also referenced under: Hadith 3819 (Reference) & Volume 4, Book 35, Hadith 3850 (DarusSalam)