Imam al-Shafi'i (may Allah have mercy on him) said: "The Messenger of Allah (peace and blessings be upon him) took the captives of Awtas and the captives of Banu al-Mustaliq, and also took men of both these tribes as prisoners, and he divided the captives. Then he (peace and blessings be upon him) ordered that no pregnant (slave woman) be approached for intercourse until she gives birth, and no non-pregnant one until she has had one menstrual period. He (peace and blessings be upon him) did not ask which of them had a husband and which did not, nor did he ask whether anyone's husband had been taken captive along with his wife or not."
Sayyiduna Abu Sa'id al-Khudri (may Allah be pleased with him) says: On the day of Awtas we obtained female captives, and the Messenger of Allah (peace and blessings be upon him) said: "No pregnant woman is to be approached for intercourse until she gives birth, nor a non-pregnant one until she has had one menstrual period."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب السير / 18297