Musannaf Ibn Abi Shayba 13:1648

Abu Bakr narrated to us, he said: Jarir narrated to us, from Mansur, from Ibrahim, regarding a slave who secretly gave dirhams to a man so that he would buy him and emancipate him. He said: If his master discovers it before he emancipates him, he (the master) is entitled to what he took of his price, and he takes back his slave. And if he discovers it after he has emancipated him, he takes from the one who bought him the equivalent of what he had taken, and he (the slave) is emancipated.