Musnad Ahmad 1018:15

Waki' narrated to us, from Sufyan, from Sa'd ibn Ibrahim, from Muhammad ibn 'Abd al-Rahman ibn Thawban, from a sheikh of the Ansar, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "It is a duty upon every Muslim to perform ghusl (full ablution), use perfume, and use the siwak on the day of Jumu'ah."