Musnad Ahmad 2:191

'Abd al-Rahman narrated to us, Sufyan narrated to us, from Qays ibn Muslim, from Tariq ibn Shihab: That the Jews said to 'Umar: "You recite a verse; if it had been revealed to us, we would have taken that day as a festival." He said: "I certainly know where it was revealed, and on what day it was revealed, and where the Messenger of Allah (peace and blessings of Allah be upon him) was when it was revealed. It was revealed on the Day of 'Arafah, and the Messenger of Allah (peace and blessings of Allah be upon him) was standing at 'Arafah." Sufyan said: "And I am in doubt whether it was a Friday or not." Meaning: "This day I have perfected for you your religion, completed My favor upon you, and have chosen for you Islam as your religion" [Al-Ma'idah: 3].