Musnad Ahmad 27:1502

Husayn ibn Muhammad narrated to us, Isra'il narrated to us, from Abu Ishaq, from Nafi' and Yahya ibn Waththab, from Ibn Umar, who said: I heard the Messenger of Allah, peace and blessings of Allah be upon him, saying upon this pulpit: "Whoever comes to the Friday prayer, let him perform ghusl (a full ritual bath)."