Yahya related to me from Malik from Nafi that Ubaydullah ibnAbdullah ibn Umar sent a question to A'isha asking her, "May a manfondle his wife when she is menstruating?" She replied, "Let her wrapher waist-wrapper around her lower part and then he may fondle her ifhe wishes."
USC-MSA web (English) reference: Book 2, Hadith 97
Arabic reference: Book 2, Hadith 127