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  

If a man has sexual intercourse (with menstruating woman) during her bleeding, he should give one dinar as sadaqah, and if he does so when bleeding has stopped, he should give half a dinar as sadaqah.  

إِذَا أَصَابَهَا فِي الدَّمِ فَدِينَارٌ وَإِذَا أَصَابَهَا فِي انْقِطَاعِ الدَّمِ فَنِصْفُ دِينَارٍ