Sa'd bin 'Ubadah asked the Messenger of Allah ﷺ about a vow which his mother had made, but she had died without fulfilling it. The Messenger of Allah ﷺ said: "Fulfill it on her behalf ."
أَنَّ سَعْدَ بْنَ عُبَادَةَ اسْتَفْتَى رَسُولَ اللَّهِ ﷺ فِي نَذْرٍ كَانَ عَلَى أُمِّهِ تُوُفِّيَتْ وَلَمْ تَقْضِهِ فَقَالَ رَسُولُ اللَّهِ ﷺ اقْضِهِ عَنْهَا