Musannaf Ibn Abi Shayba 28:248

'Abd al-Rahim ibn Sulayman narrated to us, from Ash'ath, from al-Hasan, who said: Women are not to be killed if they apostatize from Islam. Rather, they are to be invited to Islam. If they refuse, they are to be taken captive and made slave-women for the Muslims, and they are not to be killed.