Hasan al-Basri (may Allah have mercy on him) says: Everything of his wife is permissible for a man except the private part, meaning when she is menstruating. He said: The two may sleep under one quilt, meaning the menstruating woman, if there is a cloth over her private part.
Hadith Referenceالمعجم الكبير للطبراني / باب الخاء / 3982