"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.'" (Using translation from Nasāʾī 3818)
أَنَّ سَعْدَ بْنَ عُبَادَةَ اسْتَفْتَى رَسُولَ اللهِ ﷺ فِي نَذْرٍ كَانَ عَلَى أُمِّهِ تُوُفِّيَتْ قَبْلَ أَنْ تَقْضِيَهُ فَقَالَ رَسُولُ اللهِ ﷺ اقْضِ عَنْهَا