Sunan an-Nasa'i, Hadith 3656 ⓘ
It was narrated from Sa'd bin 'Ubadah that he came to the Prophet and said: "My mother has died and she had a vow to fulfill. Will it suffice if I free a slave on her behalf?" He said: "Free a slave on behalf of your mother."
أَخْبَرَنِي هَارُونُ بْنُ عَبْدِ اللَّهِ، قَالَ حَدَّثَنَا عَفَّانُ، قَالَ حَدَّثَنَا سُلَيْمَانُ بْنُ كَثِيرٍ، عَنِ الزُّهْرِيِّ، عَنْ عُبَيْدِ اللَّهِ بْنِ عَبْدِ اللَّهِ، عَنِ ابْنِ عَبَّاسٍ، عَنْ سَعْدِ بْنِ عُبَادَةَ، أَنَّهُ أَتَى النَّبِيَّ صلى الله عليه وسلم فَقَالَ إِنَّ أُمِّي مَاتَتْ وَعَلَيْهَا نَذْرٌ أَفَيُجْزِئُ عَنْهَا أَنْ أَعْتِقَ عَنْهَا قَالَ " أَعْتِقْ عَنْ أُمِّكَ " .
also referenced under: Book 30, Hadith 46 (In-Book) & Volume 4, Book 30, Hadith 3686 (DarusSalam)