Musannaf Ibn Abi Shayba 28:827

Isa ibn Yunus narrated to us, from Thawr, from Abu Awn, from Zuhrah ibn Yazid al-Muradi, that a slave woman belonging to a man among the Muslims ran away and joined the enemy, then the Muslims took her as spoils of war. Her people recognized her, so Abu Ubaydah wrote to Umar regarding her. Umar wrote: "If the slave woman has not been subjected to the one-fifth tax (khums) and has not been divided, then she is to be returned to her people. But if she has been subjected to the one-fifth tax and has been divided, then let her proceed on her way."