Musnad Ahmad 27:1867

Abu Kamil narrated to us, Zuhayr narrated to us, Abu Ishaq narrated to us, he said: I heard Nafi’ saying: Abdullah ibn Umar said: I heard the Messenger of Allah, peace and blessings of Allah be upon him, upon this pulpit saying: "Whoever comes to the Friday prayer, let him perform ghusl (ritual bath)."