Musannaf Ibn Abi Shayba 9:411

Jarir narrated to us, from Mughira, from Hammad, from Ibrahim, who said: If a Magian woman or a female idol-worshipper is taken captive, Islam is to be presented to them. If they accept Islam, they may be had sexually and employed. If they refuse to accept Islam, they are to be employed, but they are not to be had sexually.