Musannaf Ibn Abi Shayba 3:3803

Abu Usama narrated to us, from Hisham ibn Urwah, who said: A woman said to my father, "I am a pregnant woman, and it is difficult for me to pray in a *mintaq* (a waist-wrapper or belt). May I pray in a *dir'* (a chemise or long shirt) and a *khimar* (head covering)?" He said, "Yes."