Musnad Ahmad 27:1371

'Affan narrated to us, Jarir ibn Hazim narrated to us, I heard Nafi' narrate, Ibn 'Umar narrated to us, that the Messenger of Allah (ﷺ) said: "Whoever emancipates his share of a slave, if he possesses wealth that reaches the value of the slave, the slave shall be appraised at a fair value. Otherwise, he has only emancipated what he has emancipated."