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."
Muwatta Malik Book 2, Hadith 94