Ibn Umar (may Allah be pleased with them both) narrates from the Prophet (peace and blessings be upon him) that the Messenger of Allah (peace and blessings be upon him) said: "Whoever frees his share of a slave, a fair value shall be fixed for that slave, the other partners shall be given their shares, and the slave shall be free."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب العتق / 21325