Hadith 10:5
Abu Bakr narrated to us, he said: Abdullah ibn Idris narrated to us, from Hisham, from al-Hasan and Ibn Sirin, that they both said: The Sunnah divorce is before the waiting period; he divorces her while she is pure, without having had intercourse [with her during that period of purity]. And if she is pregnant, he may divorce her whenever he wishes.
حدثنا أبو بكر قال نا عبد الله بن إدريس عن هشام عن الحسن وإبن سيرين أنهما قالا طلاق السنة في قبل العدة يطلقها طاهرا في غير جماع وإن كان بها حمل طلقها متى شاء