Abu Hurairah reported the Prophet (ﷺ) as saying:
If anyone emancipates his share in a slave, he is to be completely emancipated by his money if he has money. But if he has no money, a fair price for the slave should be fixed, and the slave is required to work for his master according to the proportion of his price, but he must not be overburdened.
Abu Dawud said: In the version of both the narrators the words are "he will be required to work and must not be overburdened". This is the version of 'Ali.