The Book of Oaths
وَحَدَّثَنَا عَبْدُ بْنُ حُمَيْدٍ، حَدَّثَنَا عَبْدُ الرَّزَّاقِ، أَخْبَرَنَا مَعْمَرٌ، عَنِ الزُّهْرِيِّ، عَنْ سَالِمٍ، عَنِ ابْنِ عُمَرَ، أَنَّ النَّبِيَّ صلى الله عليه وسلم قَالَ " مَنْ أَعْتَقَ شِرْكًا لَهُ فِي عَبْدٍ عَتَقَ مَا بَقِيَ فِي مَالِهِ إِذَا كَانَ لَهُ مَالٌ يَبْلُغُ ثَمَنَ الْعَبْدِ " .Ibn 'Umar reported Allah's Apostle (ﷺ) as saying:He who gives up his share in a slave, the remaining (share) will be paid out of his riches if his riches are enough to meet the price of the slave
From Sahih Muslim, whose reports the scholars accept as authentic.