Umm al-Mu’minin Sayyidah Maymunah (may Allah be pleased with her) said: The Messenger of Allah (peace and blessings be upon him) would have intercourse with any of his wives in the state of menstruation over the izar (lower garment).
Hadith Referenceسنن دارمي / من كتاب الطهارة / 1082