حَدَّثَنَا سُفْيَانُ عَنِ عَمْرٍو عَنْ سَالِمٍ عَنْ أَبِيهِ يَبْلُغُ بِهِ النَّبِيَّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ إِذَا كَانَ الْعَبْدُ بَيْنَ اثْنَيْنِ فَأَعْتَقَ أَحَدُهُمَا نَصِيبَهُ فَإِنْ كَانَ مُوسِرًا قُوِّمَ عَلَيْهِ قِيمَةً لَا وَكْسَ وَلَا شَطَطَ ثُمَّ يُعْتَقُ
مسند امام احمد بن حنبل · Hadith 4589
It was narrated from Saalim, from his father, who attributed it to the Prophet (PBUH): "If a slave is owned by two People, and one of them frees his share (of the slave), and he is well off, a fair price should be worked out for (the slave), no more and no less, then he should be freed."