Musannaf Ibn Abi Shayba 13:741

Abu Bakr narrated to us, he said: Jarir narrated to us, from Aban ibn Taghlib, from al-Harith ibn Ibrahim and others, from Ibrahim, he said: Whoever emancipates a share that he possesses in a slave of his, whether he owns all of him or some of him, then he is entirely emancipated.