Maliks Muwatta Book 2, Hadith Number 98.
Section : What is Permitted a Man from his Wife when She is Menstruating.
Yahya related to me from Malik that he had heard that Salim ibn Abdullah and Sulayman ibn Yasar were asked whether the husband of a menstruating woman could have sexual intercourse with her when she saw that she was pure but before she had had a ghusl. They said, “No, not until she has had a ghusl.”