Musnad Abu Ya'la al-Mawsili 154:179

Shayban ibn Farrukh narrated to us, Jarir ibn Hazim narrated to us, from Nafi’, from Ibn ‘Umar, who said: The Messenger of Allah (may Allah bless him and grant him peace) said: "Whoever emancipates a share that he possesses in a slave, and he has enough wealth to reach the price of the slave, the slave shall be appraised at a fair value. Otherwise, only that which has been emancipated of him is emancipated."