حَدَّثَنِي يَحْيَى، عَنْ مَالِكٍ، عَنْ زَيْدِ بْنِ أَسْلَمَ، أَنَّ رَجُلاً، سَأَلَ رَسُولَ اللَّهِ صلى الله عليه وسلم فَقَالَ مَا يَحِلُّ لِي مِنِ امْرَأَتِي وَهِيَ حَائِضٌ فَقَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم ‏"‏ لِتَشُدَّ عَلَيْهَا إِزَارَهَا ثُمَّ شَأْنَكَ بِأَعْلاَهَا ‏"‏ ‏.‏

Yahya related to me from Malik from Zayd ibn Aslam that a manquestioned the Messenger of Allah, may Allah bless him and grant himpeace, saying, "What is permitted me from my wife when she ismenstruating?" The Messenger of Allah, may Allah bless him and granthim peace, said, "Let her wrap her waist-wrapper round herselftightly, and then what is above that is your concern." Translation Not Available

Book Ref: Muwatta Imam Malik Book 2 Hadith 125
Web Ref:  Muwatta Imam Malik Book 2 Hadith 95