Musannaf Ibn Abi Shayba 28:757

'Abd al-Rahim ibn Sulayman narrated to us, from 'Abd al-Malik ibn Abi Sulayman, from 'Ata' ibn al-Sa'ib, from al-Sha'bi, from 'Abdah, regarding the verse: "They ask you about the spoils of war" (al-Anfal). He said: Whatever strayed from the polytheists of the enemy to the Muslims, whether it be a slave, goods, or an animal, it is the spoils (al-anfal) which the Imam decides upon as he likes.