أَخْبَرَنَا قُتَيْبَةُ بْنُ سَعِيدٍ، قَالَ حَدَّثَنَا اللَّيْثُ، عَنِ الزُّهْرِيِّ، عَنْ عُبَيْدِ اللَّهِ بْنِ عَبْدِ اللَّهِ، عَنِ ابْنِ عَبَّاسٍ، قَالَ اسْتَفْتَى سَعْدُ بْنُ عُبَادَةَ الأَنْصَارِيُّ 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 Al-Ansari consulted the Messenger of Allah about an (outstanding) vow that his mother had to fulfill, but she died before doing so. The Messenger of Allah said: 'Fulfill it on her behalf.'" Translation Not Available

Book Ref: Sunan An Nisai Book 30 Hadith 3662
Web Ref:  Sunan An Nisai Vol 4 Book 30 Hadith 3692