Musnad Ahmad 1163:24

Yazid ibn Harun narrated to us, he said: Muhammad ibn Ishaq informed us, from al-Zuhri, from Urwah, from Nadbah, who said: Maymunah bint al-Harith sent me to the wife of Abdullah ibn Abbas, and there was a kinship between them. I saw her bedding separated from his bedding, so I thought that was due to estrangement. I asked her, and she said: "No, but I am menstruating. When I menstruate, he does not approach my bedding." I came to Maymunah and mentioned that to her. She sent me back to Ibn Abbas, and she said: "Is it a turning away from the Sunnah of the Messenger of Allah (peace and blessings of Allah be upon him)? The Messenger of Allah (peace and blessings of Allah be upon him) used to sleep with a woman from his wives while she was menstruating, and there was nothing between them except a garment that did not go beyond the knees."