Sahih Muslim
The Book of Oaths (Kitab Al-Aiman)
Book Number: 015 / Hadith Number: 4104
'Abdullah b. 'Umar reported Allah's Messenger (may peace be upon him) as saying: He who gives up his share in a slave, and he has money enough to meet the full price, a fair price for him should be fixed; otherwise be has emancipated him to the extent that he has emancipated.