Sayyiduna Abu Hurayrah (may Allah be pleased with him) says that the Messenger of Allah (peace and blessings be upon him) was asked about a slave of whom one share had been freed. He said: "The slave is indeed free, but the value is to be charged to the owner of that share. If he is wealthy, well and good; otherwise the slave is to be made to work, but without being overburdened."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب العتق / 21371