Musnad Ahmad 27:1909

'Abd al-Razzaq and Ibn Bakr narrated to us, they said: Ibn Jurayj informed us, he said: Ibn Shihab informed me, from Salim ibn 'Abd Allah, from Ibn 'Umar, from the Messenger of Allah (peace and blessings of Allah be upon him), who said: "Whoever among you comes to the Friday [prayer], let him perform ghusl (a ritual bath)."