Language:
كتاب الإيمان
2
Belief
(33)
Chapter: Faith increases and decreases
(33)
باب زِيَادَةِ الإِيمَانِ وَنُقْصَانِهِ
وَقَوْلِ اللَّهِ تَعَالَى: {وَزِدْنَاهُمْ هُدًى}، {وَيَزْدَادَ الَّذِينَ آمَنُوا إِيمَانًا} وَقَالَ: {الْيَوْمَ أَكْمَلْتُ لَكُمْ دِينَكُمْ} فَإِذَا تَرَكَ شَيْئًا مِنَ الْكَمَالِ فَهُوَ نَاقِصٌ.

Narrated 'Umar bin Al-Khattab:

Once a Jew said to me, "O the chief of believers! There is a verse in your Holy Book Which is read by all of you (Muslims), and had it been revealed to us, we would have taken that day (on which it was revealed as a day of celebration." 'Umar bin Al-Khattab asked, "Which is that verse?" The Jew replied, "This day I have perfected your religion For you, completed My favor upon you, And have chosen for you Islam as your religion." (5:3) 'Umar replied,"No doubt, we know when and where this verse was revealed to the Prophet. It was Friday and the Prophet (ﷺ) was standing at 'Arafat (i.e. the Day of Hajj)"

حَدَّثَنَا الْحَسَنُ بْنُ الصَّبَّاحِ، سَمِعَ جَعْفَرَ بْنَ عَوْنٍ، حَدَّثَنَا أَبُو الْعُمَيْسِ، أَخْبَرَنَا قَيْسُ بْنُ مُسْلِمٍ، عَنْ طَارِقِ بْنِ شِهَابٍ، عَنْ عُمَرَ بْنِ الْخَطَّابِ، أَنَّ رَجُلاً، مِنَ الْيَهُودِ قَالَ لَهُ يَا أَمِيرَ الْمُؤْمِنِينَ، آيَةٌ فِي كِتَابِكُمْ تَقْرَءُونَهَا لَوْ عَلَيْنَا مَعْشَرَ الْيَهُودِ نَزَلَتْ لاَتَّخَذْنَا ذَلِكَ الْيَوْمَ عِيدًا‏.‏ قَالَ أَىُّ آيَةٍ قَالَ ‏{‏الْيَوْمَ أَكْمَلْتُ لَكُمْ دِينَكُمْ وَأَتْمَمْتُ عَلَيْكُمْ نِعْمَتِي وَرَضِيتُ لَكُمُ الإِسْلاَمَ دِينًا‏}‏‏.‏ قَالَ عُمَرُ قَدْ عَرَفْنَا ذَلِكَ الْيَوْمَ وَالْمَكَانَ الَّذِي نَزَلَتْ فِيهِ عَلَى النَّبِيِّ صلى الله عليه وسلم وَهُوَ قَائِمٌ بِعَرَفَةَ يَوْمَ جُمُعَةٍ‏.‏
Reference : Sahih al-Bukhari 45
In-book reference : Book 2, Hadith 38
USC-MSA web (English) reference : Vol. 1, Book 2, Hadith 44
  (deprecated numbering scheme)