It is narrated from Hazrat Aisha (may Allah be pleased with her) that when the Prophet (peace and blessings be upon him) wanted to be intimate with any of us and she was in her menstrual period, the Prophet (peace and blessings be upon him) would be intimate with his wives over the lower garment. And when he wanted to sleep in a state requiring ghusl (ritual bath), he would perform ablution as for prayer.