Al-Baqarah · 2:222

222. O Prophet! Your Companions ask you about menses (which is the blood of menstruation that naturally comes out of the womb at certain times of the month). Say in reply to them: Menses is harmful to the man and woman, so avoid sexual intercourse during this time. Do not approach them for sexual intercourse until the blood stops and they have cleaned themselves by taking a bath. If the blood has stopped and they have cleaned themselves, then you may have sexual intercourse with them through the vagina in the manner that Allah has permitted for you. Allah loves those that frequently repent from their sins and are extra mindful of cleanliness.