Some Jews said, "If this verse had been revealed about us, we would have made that day a festival."Umar asked, "Which verse?"They said, "Today I have perfected your religion for you and completed My favor upon you" [Maidah 5:3].Umar said, "I know exactly where it was revealed. It was revealed while the Messenger of Allah ﷺ was standing at Arafah."
أن أناسا من اليهود قالوا: لو نزلت هذه الآية فينا لاتخذنا ذلك اليوم عيدا. فقال: عمر أية آية؟ فقالوا: {اليوم أكملت لكم دينكم وأتممت عليكم نعمتي} [المائدة: ٣]، فقال عمر: إني لأعلم أي مكان أنزلت، أنزلت ورسول الله ﷺ واقف بعرفة.
Bukhari narrated it in the Book of Military Expeditions (4407), and Muslim in the Book of Tafsir (3017), both from the hadith of Sufyan Thawri, from Qays bin Muslim, from Tariq bin Shihab, who mentioned it. The wording given is that of Bukhari.