It was narrated from Ibn 'Abbas' that :
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 ."

حَدَّثَنَا مُحَمَّدُ بْنُ رُمْحٍ، أَنْبَأَنَا اللَّيْثُ بْنُ سَعْدٍ، عَنِ ابْنِ شِهَابٍ، عَنْ عُبَيْدِ اللَّهِ بْنِ عَبْدِ اللَّهِ، عَنِ ابْنِ عَبَّاسٍ، أَنَّ سَعْدَ بْنَ عُبَادَةَ، اسْتَفْتَى رَسُولَ اللَّهِ ـ ﷺ ـ فِي نَذْرٍ كَانَ عَلَى أُمِّهِ تُوُفِّيَتْ وَلَمْ تَقْضِهِ فَقَالَ رَسُولُ اللَّهِ ـ ﷺ ـ " اقْضِهِ عَنْهَا " .