Abu Huraira (Allah be pleased with him) reported Allah's Messenger (ﷺ) as saying:The slave who is jointly owned by two persons, and is emancipated by one of them, (this one) has liability (upon him to secure complete freedom for that slave).
وَحَدَّثَنَا مُحَمَّدُ بْنُ الْمُثَنَّى، وَابْنُ، بَشَّارٍ - وَاللَّفْظُ لاِبْنِ الْمُثَنَّى - قَالاَ حَدَّثَنَا مُحَمَّدُ، بْنُ جَعْفَرٍ حَدَّثَنَا شُعْبَةُ، عَنْ قَتَادَةَ، عَنِ النَّضْرِ بْنِ أَنَسٍ، عَنْ بَشِيرِ بْنِ نَهِيكٍ، عَنْ أَبِي هُرَيْرَةَ، عَنِ النَّبِيِّ صلى الله عليه وسلم قَالَ فِي الْمَمْلُوكِ بَيْنَ الرَّجُلَيْنِ فَيُعْتِقُ أَحَدُهُمَا قَالَ " يَضْمَنُ" .
Muslim
The Book of Emancipating Slaves • Hadith 3