Mukhtasar Bukhari

Narrated Abu Huraira (may Allah be pleased with him) from the Prophet (peace and blessings of Allah be upon him) that he said: "Whoever frees his (jointly owned) slave to the extent of his share, it is necessary for him to secure the slave's complete freedom from his own wealth. Then, if he does not have enough wealth, the value of the slave should be estimated by a just person, and the slave should be made to work to pay it off, but he should not be forced (for this work)."