Musannaf Ibn Abi Shayba 28:234

'Abd al-Rahim ibn Sulayman narrated to us, from Ash'ath, from 'Amir and al-Hakam, who both said regarding the Muslim man who apostatizes from Islam and joins the land of the enemy: His wife shall observe a waiting period ('iddah) of three menstrual cycles if she menstruates. If she does not menstruate, then three months. And if she is pregnant, until she delivers her burden. His inheritance shall be divided between his wife and his heirs among the Muslims. Then she may marry if she wishes. And if he returns and repents before her waiting period has expired, they remain upon their marriage.