ENOfficial
Muhammad bin 'Abdullah bin Yazid said: "Sufyan narrated to us from Az-Zuhri, from 'Ubaidullah bin 'Abdullah, from Ibn 'Abbas, that Sa'd said: 'My mother died and there was an (outstanding) vow that she had to fulfill. I asked the Prophet (ﷺ) and he told me to fulfill it on her behalf.'"
Source: sunnah.com
Other translations
Arabic
أَخْبَرَنَا مُحَمَّدُ بْنُ عَبْدِ اللَّهِ بْنِ يَزِيدَ، قَالَ حَدَّثَنَا سُفْيَانُ، عَنِ الزُّهْرِيِّ، عَنْ عُبَيْدِ اللَّهِ بْنِ عَبْدِ اللَّهِ، عَنِ ابْنِ عَبَّاسٍ، عَنْ سَعْدٍ، أَنَّهُ قَالَ مَاتَتْ أُمِّي وَعَلَيْهَا نَذْرٌ فَسَأَلْتُ النَّبِيَّ صلى الله عليه وسلم فَأَمَرَنِي أَنْ أَقْضِيَهُ عَنْهَا.
sunnah.com