Musnad Ahmad 188
It was narrated that Tariq bin Shihab said:
A Jewish man came to 'Umar and said: O Ameer al-Mu'mineen, you read a verse in your Book which, if it had been revealed to us Jews, we would have taken that day as a festival. He said: Which verse is it? He said: The verse: `This day, I have perfected your religion for you, completed My Favour upon you” (al Ma'idah 5:3]. 'Umar said: By Allah, I know the day on which this was revealed to the Messenger of Allah ﷺ and the hour at which it was revealed to the Messenger of Allah ﷺ,  on the afternoon of 'Arafah on a Friday.
حَدَّثَنَا جَعْفَرُ بْنُ عَوْنٍ، أَنْبَأَنَا أَبُو عُمَيْسٍ، عَنْ قَيْسِ بْنِ مُسْلِمٍ، عَنْ طَارِقِ بْنِ شِهَابٍ، قَالَ جَاءَ رَجُلٌ مِنْ الْيَهُودِ إِلَى عُمَرَ رَضِيَ اللَّهُ عَنْهُ فَقَالَ يَا أَمِيرَ الْمُؤْمِنِينَ إِنَّكُمْ تَقْرَءُونَ آيَةً فِي كِتَابِكُمْ لَوْ عَلَيْنَا مَعْشَرَ الْيَهُودِ نَزَلَتْ لَاتَّخَذْنَا ذَلِكَ الْيَوْمَ عِيدًا قَالَ وَأَيُّ آيَةٍ هِيَ قَالَ قَوْلُهُ عَزَّ وَجَلَّ ‏{‏الْيَوْمَ أَكْمَلْتُ لَكُمْ دِينَكُمْ وَأَتْمَمْتُ عَلَيْكُمْ نِعْمَتِي‏}‏ قَالَ فَقَالَ عُمَرُ رَضِيَ اللَّهُ عَنْهُ وَاللَّهِ إِنَّنِي لَأَعْلَمُ الْيَوْمَ الَّذِي نَزَلَتْ فِيهِ عَلَى رَسُولِ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ وَالسَّاعَةَ الَّتِي نَزَلَتْ فِيهَا عَلَى رَسُولِ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ عَشِيَّةَ عَرَفَةَ فِي يَوْمِ الْجُمُعَةِ‏.‏