Chapter 57: The Book of Commentary on the Qur'an
Tariq b. Shihab reported that a Jew said to' Umar: You recite a verse which, if it had been revealed in relation to us, we would have taken that day as the day of rejoicing. Thereupon 'Umar said: I know where it was revealed and on the day when it was revealed and where Allah' s Messenger (ﷺ) had been at that time when it was revealed. It was revealed on the day of 'Arafa (ninth of Dhu' l Hijjah) and Allah' s Messenger (ﷺ) had been staying in 'Arafat. Sufyan said: I doubt, whether it was Friday or not (and the verse referred to) is this: " Today I have perfected your religion for you and completed My favours upon you" (v. 4).
Sahih Muslim 3017a