Sahih Muslim 3017 a
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).
حَدَّثَنِي أَبُو خَيْثَمَةَ، زُهَيْرُ بْنُ حَرْبٍ وَمُحَمَّدُ بْنُ الْمُثَنَّى - وَاللَّفْظُ لاِبْنِ الْمُثَنَّى - قَالاَ حَدَّثَنَا عَبْدُ الرَّحْمَنِ، - وَهُوَ ابْنُ مَهْدِيٍّ - حَدَّثَنَا سُفْيَانُ، عَنْ قَيْسِ بْنِ مُسْلِمٍ، عَنْ طَارِقِ، بْنِ شِهَابٍ أَنَّ الْيَهُودَ، قَالُوا لِعُمَرَ إِنَّكُمْ تَقْرَءُونَ آيَةً لَوْ أُنْزِلَتْ فِينَا لاَتَّخَذْنَا ذَلِكَ الْيَوْمَ عِيدًا ‏.‏ فَقَالَ عُمَرُ إِنِّي لأَعْلَمُ حَيْثُ أُنْزِلَتْ وَأَىَّ يَوْمٍ أُنْزِلَتْ وَأَيْنَ رَسُولُ اللَّهِ صلى الله عليه وسلم حَيْثُ أُنْزِلَتْ أُنْزِلَتْ بِعَرَفَةَ وَرَسُولُ اللَّهِ صلى الله عليه وسلم وَاقِفٌ بِعَرَفَةَ ‏.‏ قَالَ سُفْيَانُ أَشُكُّ كَانَ يَوْمَ جُمُعَةٍ أَمْ لاَ ‏.‏ يَعْنِي ‏{‏ الْيَوْمَ أَكْمَلْتُ لَكُمْ دِينَكُمْ وَأَتْمَمْتُ عَلَيْكُمْ نِعْمَتِي‏}‏