Allah, the Blessed and Exalted, says: "So keep away from women during menstruation, and do not approach them until they are purified." [Surah al-Baqarah: 222]
Nafi' narrates from Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) that he sent me to Sayyidah Aishah (may Allah be pleased with her) to ask: may a man be intimate with his wife while she is menstruating? She said: She should tie her lower garment (izar) firmly over her lower body, then he may be intimate with her if he wishes.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب النكاح / 14080