Musannaf Ibn Abi Shayba 9:235

'Abd al-'Aziz ibn 'Abd al-Samad al-'Ammi narrated to us, from 'Ata' ibn al-Sa'ib, from Ibrahim: That Ibn Mas'ud said regarding a man—meaning a slave—who divorced his wife two pronouncements while she was a slave, and then they were both emancipated: Ibn Mas'ud said: He shall not marry her until she has married a husband other than him.