Musnad Ahmad 27:471

'Abd al-Razzaq narrated to us, Ma'mar informed us, from al-Zuhri, from Salim, from Ibn 'Umar, who said: I heard the Messenger of Allah, peace and blessings of Allah be upon him, while he was on the pulpit, saying: "Whoever among you comes to the Friday [prayer], let him perform ghusl (a ritual bath)."