There should be no sexual intercourse with a pregnant woman until she gives birth, nor with a non-pregnant woman until she has one menstrual cycle
Authentic hadithعن أبي سعيد رضي الله عنه أن النبي صلى الله عليه وسلم قال في سَبَايَا أَوْطَاس: «لا تُوطَأُ حَامِلٌ حتى تَضَعَ، ولا غَيْرُ ذَاتِ حَمْلٍ حتى تَحِيضَ حَيْضَةً».
Abu Sa‘īd al-Khudri (may Allah be pleased with him) reported that the Prophet (may Allah's peace and blessings be upon him) said regarding the female captives of Awtās: ''There should be no sexual intercourse with a pregnant woman until she gives birth, nor with a non-pregnant woman until she has one menstrual cycle."
Explanation
Abu Sa‘īd al-Khudri (may Allah be pleased with him) reported that in Awtās, a place close to Makkah, the Prophet (may Allah's peace and blessings be upon him) forbade having sexual intercourse with women taken as captives in the course of jihad until their wombs were clear, such that pregnant women would give birth and attain purity of the postpartum bleeding; and non-pregnant women have one menstrual cycle. This also applies to the female captives who were bought and the female slaves who were owned in any way.
Source · Narrated by Abu Daoud - Narrated by Ahmad - Ad-Daarimi
From the Hadith Encyclopedia (hadeethenc.com).