It was narrated that Anas bin Malik said:
“The Messenger of Allah ﷺ granted a concession to pregnant women who fear for themselves, allowing them not to fast, and to nursing mothers who fear for their infants.”

حَدَّثَنَا هِشَامُ بْنُ عَمَّارٍ الدِّمَشْقِيُّ، حَدَّثَنَا الرَّبِيعُ بْنُ بَدْرٍ، عَنِ الْجُرَيْرِيِّ، عَنِ الْحَسَنِ، عَنْ أَنَسِ بْنِ مَالِكٍ، قَالَ رَخَّصَ رَسُولُ اللَّهِ ﷺ لِلْحُبْلَى الَّتِي تَخَافُ عَلَى نَفْسِهَا أَنْ تُفْطِرَ وَلِلْمُرْضِعِ الَّتِي تَخَافُ عَلَى وَلَدِهَا .