مُوَطَّأُ مَالِكٍ
Muwatta Malik 128
Purity
وَحَدَّثَنِي عَنْ مَالِكٍ، أَنَّهُ بَلَغَهُ أَنَّ سَالِمَ بْنَ عَبْدِ اللَّهِ، وَسُلَيْمَانَ بْنَ يَسَارٍ، سُئِلاَ عَنِ الْحَائِضِ، هَلْ يُصِيبُهَا زَوْجُهَا إِذَا رَأَتِ الطُّهْرَ قَبْلَ أَنْ تَغْتَسِلَ فَقَالاَ لاَ حَتَّى تَغْتَسِلَ .
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."
Arabic/English book reference: Book 2, Hadith 98