Abu Dawud Book 24, Hadith Number 3926.

Chapter : The view that the slave will be required to work to pay the price of the remaining portion.

Narated By N/A : Abu Hurairah reported the Prophet (may peace be upon him) as saying: If anyone emancipates a share in his slave, he should completely emancipate him if he has money; but if he has none, the slave will be required to work (to pay for his free-dom), but he must not be overburdened.