Musannaf Ibn Abi Shayba 1:759

Ibn ‘Uyaynah narrated to us, from Yahya ibn Sa’id, who said: A man asked Sa’id ibn al-Musayyib, "Do you see, if I perform the ghusl (full body wash) for janabah (major ritual impurity), does it suffice me from wudu (ablution)?" He said, "Yes, but wash your feet."