Musannaf Ibn Abi Shayba 28:1073

Isma'il ibn 'Ayyash narrated to us, from 'Abd al-Rahman ibn Yazid and Muhammad ibn 'Abd Allah al-Shu'aythi, from Makhul, who said: Whatever you cut from the land of the enemy, and you fashioned from it a bowl, a peg, a club, or a sledgehammer, then there is no harm in it. And whatever you found of that already fashioned, then return it to the spoils of war.