Abu Sa’id Al Khudri traced to Prophet ﷺ the following statement regarding the captives taken at Atwas. There must be no intercourse with pregnant woman till she gives birth to her child or with the one who is not pregnant till she has had one menstrual period. (Using translation from Abū Dāʾūd 2157)   

أَنَّهُ قَالَ فِي سَبَايَا أَوْطَاسٍ لَا تُوطَأْ حَامِلٌ حَتَّى تَضَعَ وَلَا غَيْرُ ذَاتِ حَمْلٍ حَتَّى تَحِيضَ حَيْضَةً  

[Machine] The Messenger of Allah ﷺ does not touch a woman who is pregnant until she gives birth, nor [does he touch] a woman who is not pregnant until she menstruates. This statement is supported by the evidence that has been mentioned, and we have narrated from Abdullah ibn Mas'ood that he said: "A female slave is to be freed if she is purchased while menstruating."  

رَسُولُ اللهِ ﷺ لَا يَمَسَّ رَجُلٌ امْرَأَةً حُبْلَى حَتَّى تَضَعَ حَمْلَهَا وَلَا غَيْرَ ذَاتِ حَمْلٍ حَتَّى تَحِيضَ حَيْضَةً وَهَذَا الْمُرْسَلُ شَاهِدٌ لِمَا تَقَدَّمَ وَرُوِّينَا عَنْ عَبْدِ اللهِ بْنِ مَسْعُودٍ أَنَّهُ قَالَ تُسْتَبْرَأُ الْأَمَةُ إِذَا اشْتُرِيَتْ بِحَيْضَةٍ