Musannaf Ibn Abi Shayba 28:996

Muhammad ibn Bakr narrated to us, from Ibn Jurayj, who said: 'Ata’ said regarding the free person whom the enemy captures and then a Muslim purchases: "It is like his statement regarding women." And ‘Amr ibn Dinar said the same thing, meaning: "He gives them themselves [their freedom] for the price for which he purchased them."