Musnad Ahmad 313:2

Muhammad ibn Ja‘far narrated to us, Shu‘bah narrated to us, from Sa‘d ibn Ibrahim, who said: I heard Muhammad ibn ‘Abd al-Rahman ibn Thawban narrating from a man of the Ansar, from a man among the companions of the Prophet, may Allah bless him and grant him peace, that he said: "Three things are a duty upon every Muslim: bathing on the day of Friday, the tooth-stick (siwak), and applying some perfume if he finds any."