It was narrated from Ibn 'Abbas that:
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." (RU)
English reference (RU): Vol. 1, Book 1, Hadith 640 (RU)
Arabic reference (RU): Book 1, Hadith 683 (RU)