Whoever frees his share of a common slave and he has sufficient money to free him completely, should let its price be estimated by a just man and give his partners the price of their shares and manumit the slave
Authentic hadithعن عَبْدُ الله بن عمر رضي الله عنهما عن النبي صلى الله عليه وسلم قال: «مَن أَعْتَقَ شِرْكًا له في عَبْدٍ، فكان له مالٌ يَبْلُغُ ثَمَنَ العَبْدِ: قُوِّمَ عليه قِيمَةَ عَدْلٍ ، فأعطى شُرَكَاءَهُ حِصَصَهُمْ، وعَتَقَ عليه العَبْدُ ، وإلا فقد عَتَقَ منه ما عَتَقَ».
‘Abdullah ibn ‘Umar (may Allah be pleased with him) reported that the Messenger of Allah (may Allah's peace and blessings be upon him) said: "Whoever frees his share of a common slave and he has sufficient money to free him completely, should let its price be estimated by a just man and give his partners the price of their shares and manumit the slave; otherwise (i.e. if he has not sufficient money) he manumits the slave partially."
Explanation
If a person has a share, albeit small, to the ownership of a slave, male or female, and he manumits part of it, the slave will be manumitted as much as this part. If the manumitter is well-to-do enough to afford to pay the share of his partner, he ought to manumit the slave wholly, assessing his partner's market value and giving it to him. If he is not that rich, however, he can manumit the slave partially, as much as his share in his ownership, with the rest remaining in bondage.
Source · Narrated by Bukhari & Muslim
From the Hadith Encyclopedia (hadeethenc.com).