Sunan an-Nasa'i, Volume 4, Book 35, Hadith 3848 (DarusSalam) ⓘ

It was narrated from Ibn 'Abbas that 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. He said: "Fulfill it on her behalf."

أَخْبَرَنَا عَلِيُّ بْنُ حُجْرٍ، وَالْحَارِثُ بْنُ مِسْكِينٍ، قِرَاءَةً عَلَيْهِ وَأَنَا أَسْمَعُ، - وَاللَّفْظُ لَهُ - عَنْ سُفْيَانَ، عَنِ الزُّهْرِيِّ، عَنْ عُبَيْدِ اللَّهِ بْنِ عَبْدِ اللَّهِ، عَنِ ابْنِ عَبَّاسٍ، أَنَّ سَعْدَ بْنَ عُبَادَةَ، اسْتَفْتَى رَسُولَ اللَّهِ صلى الله عليه وسلم فِي نَذْرٍ كَانَ عَلَى أُمِّهِ تُوُفِّيَتْ قَبْلَ أَنْ تَقْضِيَهُ فَقَالَ ‏ "‏ اقْضِهِ عَنْهَا ‏" ‏ ‏.‏