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]
Hadith Referenceالسنن الكبرى للبيهقي / كتاب النكاح / Q14080
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
Zayd bin Aslam (may Allah have mercy on him) said that a man asked the Messenger of Allah (peace and blessings be upon him): What is lawful for me from my wife when she is menstruating? He (peace and blessings be upon him) said: "Let her tie her lower garment (izar) firmly over her lower body; then the upper part is yours to do as you wish."
This is mursal.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب النكاح / 14081
Sayyidah Aishah (may Allah be pleased with her) narrates from the Prophet (peace and blessings be upon him) that the Messenger of Allah (peace and blessings be upon him) was asked: What is permissible for a man when his wife is menstruating? He (peace and blessings be upon him) said: "Whatever is above the lower garment (izar)."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب النكاح / 14082
Ata bin Yasar narrates from Sayyidah Aishah (may Allah be pleased with her) that she was with the Prophet (peace and blessings be upon him) under one blanket. I slipped away quietly, and the Prophet (peace and blessings be upon him) asked: "What is the matter with you?" I said: I have begun my menses. He (peace and blessings be upon him) said: "Tie your waist-wrap on, then come back in."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب النكاح / 14083
Sayyidah Maymunah (may Allah be pleased with her) said: When the Messenger of Allah (peace and blessings be upon him) wished to be intimate with (i.e. lie close to) a wife of his while she was menstruating, he would instruct that "she tie her waist-wrap tightly."
Imam al-Shafi'i (may Allah have mercy on him) said: Some people disagreed with us about a man's intimacy with his wife and his coming close to her while she is menstruating, and said: We have narrated the opposite of what you have narrated; we narrated that he should keep away from the place of the blood and then take whatever (enjoyment) he wishes. And he cited a hadith that the people of knowledge of hadith do not regard as established.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب النكاح / 14084