Yahya related to me from Malik from Safwan ibn Sulaym from Ataibn Yasar from Abu Said al-Khudri that the Messenger of Allah, mayAllah bless him and grant him peace, said, "Ghusl on the day of jumuais incumbent on every male who has reached puberty."
USC-MSA web (English) reference: Book 5, Hadith 4
Arabic reference: Book 5, Hadith 229