Hadith 2332
It is narrated from Sayyiduna Abu Sa'id Khudri (may Allah be pleased with him) in a marfu' form that the Messenger of Allah (peace and blessings be upon him) said regarding the captives of Autas: "No pregnant woman should be approached (for intercourse) until she has given birth (i.e., intercourse should only take place after she has delivered and is in a state of purity), and no non-pregnant woman should be approached until she has had one menstrual cycle (so that it becomes clear she is not pregnant)."