Musannaf Ibn Abi Shayba 1:665

Waki’ narrated to us, from Hisham al-Dastawa’i and Ibn Abi ‘Aruba, from Qatada, from Sa’id ibn al-Musayyib, who said: If a person in a state of major ritual impurity (junub) wishes to eat, he should wash his hands and rinse his mouth.