Maliks Muwatta Book 5, Hadith Number 4.
Section : Doing Ghusl on the Day of Jumua.
Yahya related to me from Malik from Safwan ibn Sulaym from Ata ibn Yasar from Abu Said al-Khudri that the Messenger of Allah, may Allah bless him and grant him peace, said, “Ghusl on the day of jumua is incumbent on every male who has reached puberty.”