Sayyidah Aishah (may Allah be pleased with her) says that the Messenger of Allah (peace and blessings be upon him) said: "The Day of Arafah is when the imam stands at Arafah, the day of Eid al-Adha is the day the imam sacrifices, and Eid al-Fitr is the day the imam breaks the fast."
This Muhammad is known as al-Farisi; he was a Kufan and the judge of Fars, and he alone narrated it from Sufyan.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الحج / 9827