Musnad Abu Ya'la al-Mawsili 110:105

From Abu Ja'far, from 'Abd al-Karim ibn Abi al-Mukhariq, from Miqsam, from Ibn 'Abbas, from the Prophet (may Allah bless him and grant him peace), regarding a man who had intercourse with his wife while she was menstruating. He said: "If it was fresh blood, then let him give a dinar in charity. And if it was yellowish, then half a dinar."