Musannaf Ibn Abi Shayba 3:2614

4991. Shareek and Abu al-Ahwas narrated to us, from Abu Ishaq, from Yahya ibn Wathab, from Ibn Umar, who said: The Messenger of Allah (may Allah bless him and grant him peace) said: "Whoever comes to the Friday [prayer], let him perform ghusl (a ritual bath)."