Musnad Ahmad 2:315

Ishaq ibn Isa narrated to us, Malik informed us, from Nafi, from Ibn Umar, that the Messenger of Allah (peace and blessings of Allah be upon him) said: "Whoever emancipates his share in a slave, and he possesses what reaches the price of the slave, then the slave shall be appraised at a fair value, and his partners shall be given their due right, and the slave is emancipated for him. But if he does not possess that, then he has only emancipated what he has emancipated."