Maliks Muwatta Book 2, Hadith Number 97.

Section : What is Permitted a Man from his Wife when She is Menstruating.

Yahya related to me from Malik from Nafi that Ubaydullah ibn Abdullah ibn Umar sent a question to A’isha asking her, “May a man fondle his wife when she is menstruating?” She replied, “Let her wrap her waist-wrapper around her lower part and then he may fondle her if he wishes.”