Sayyiduna Ibn Umar (may Allah be pleased with them both) says that the Messenger of Allah (peace and blessings be upon him) said: "Whoever frees his share in a slave and has wealth equal to the slave's price, the slave's value shall be assessed, the other partners shall be given their shares, and the slave shall be free. Otherwise, only as much is freed as he has freed."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب العتق / 21322