Hadith 501250
Chapter 2: Purity - كتاب الطهارة
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 man questioned the Messenger of Allah, may Allah bless him and grant him peace, saying, "What is permitted me from my wife when she is menstruating?" The Messenger of Allah, may Allah bless him and grant him peace, said, "Let her wrap her waist-wrapper round herself tightly, and then what is above that is your concern."
Reference Muwatta Malik 501250
USC-MSA web (English) reference : Book 2, Hadith 95