It is narrated from Nafi' bin Jubair and 'Ata bin Yasar, may Allah have mercy on them, that they narrate from the Prophet ﷺ that he ﷺ said: "The witnessed day is the day of Jumu'ah, and the attended day is the day of 'Arafah."
Hadith Referenceمسند الإمام الشافعي / كتاب الجمعة / 399