Musannaf Ibn Abi Shayba 3:2611

Abu Bakr narrated to us, he said: Sufyan ibn 'Uyaynah narrated to us, from Safwan ibn Sulaym, from 'Ata' ibn Yasar, from Abu Sa'id al-Khudri, who said: The Messenger of Allah (may Allah bless him and grant him peace) said: "Ghusl (full ritual washing) on the day of Jumu'ah is obligatory upon every person who has reached puberty."