Sahih al Bukhari 331
Menstrual Periods
حَدَّثَنَا أَحْمَدُ بْنُ يُونُسَ، عَنْ زُهَيْرٍ، قَالَ حَدَّثَنَا هِشَامٌ، عَنْ عُرْوَةَ، عَنْ عَائِشَةَ، قَالَتْ قَالَ النَّبِيُّ صلى الله عليه وسلم " إِذَا أَقْبَلَتِ الْحَيْضَةُ فَدَعِي الصَّلاَةَ، وَإِذَا أَدْبَرَتْ فَاغْسِلِي عَنْكِ الدَّمَ وَصَلِّي ".
Narrated `Aisha:The Prophet (ﷺ) said to me, "Give up the prayer when your menses begin and when it has finished, wash the blood off your body (take a bath) and start praying
Text from the public-domain hadith-api dataset. Numbering follows that dataset and can differ by a few from some printed editions — check the wording, not only the number.