"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)
اسْتَفْتَى سَعْدُ بْنُ عُبَادَةَ رَسُولَ اللهِ ﷺ فِي نَذْرٍ عَلَى أُمِّهِ تُوُفِّيَتْ قَبْلَ أَنْ تَقْضِيَهُ؟ فَقَالَ رَسُولُ اللهِ ﷺ اقْضِهِ عَنْهَا