The Prophet ﷺ said about a man who has sexual intercourse with a menstruating woman: He should give one or half dinar as sadaqah.

عَنِ النَّبِيِّ ﷺ فِي الَّذِي يَأْتِي امْرَأَتَهُ وَهِيَ حَائِضٌ قَالَ يَتَصَدَّقُ بِدِينَارٍ أَوْ بِنِصْفِ دِينَارٍ