The Prophet said concerning one who has intercourse with a woman when she is menstruating: "Let him give a Dinar or half a Dinar in charity."  

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