Musnad Ahmad 31:822

Aswad ibn Amir narrated to us, Sharik narrated to us, from Abu Ishaq, from Abu al-Wadak, from Abu Sa’id, and Qays ibn Wahb, from Abu al-Wadak, from Abu Sa’id, who said: The Prophet, peace and blessings of Allah be upon him, said during the Battle of Awtas: "A pregnant woman shall not be had intercourse with until she delivers, and a woman who is not pregnant shall not be had intercourse with until she has one menstrual cycle."