Abu Talha reported:

'Umar b. al-Khattab (Allah be pleased with him) delivered a sermon on Friday and made a mention of Allah's Apostle (ﷺ) and he also made a mention of Abu Bakr (Allah be pleased with him) and then said: I do not leave behind me any problem more difficult than that of Kalala. I did not refer to Allah's Messenger (ﷺ) more repeatedly than in case of the problem of Kalala, and he (the Holy Prophet) never showed more annoyance to me than in regard to this problem, so much so that he struck my chest with his fingers and said: 'Umar, does the verse revealed in summer season, at the end of Sura al-Nisa' not suffice you? Hadrat 'Umar (then) said: If I live I would give such verdict about (Kalala) that everyone would be able to decide whether he reads the Qur'an or he does not.
حَدَّثَنَا مُحَمَّدُ بْنُ أَبِي بَكْرٍ الْمُقَدَّمِيُّ، وَمُحَمَّدُ بْنُ الْمُثَنَّى، - وَاللَّفْظُ لاِبْنِ الْمُثَنَّى - قَالاَ حَدَّثَنَا يَحْيَى بْنُ سَعِيدٍ، حَدَّثَنَا هِشَامٌ، حَدَّثَنَا قَتَادَةُ، عَنْ سَالِمِ بْنِ أَبِي الْجَعْدِ، عَنْ مَعْدَانَ بْنِ، أَبِي طَلْحَةَ أَنَّ عُمَرَ بْنَ الْخَطَّابِ، خَطَبَ يَوْمَ جُمُعَةٍ فَذَكَرَ نَبِيَّ اللَّهِ صلى الله عليه وسلم وَذَكَرَ أَبَا بَكْرٍ ثُمَّ قَالَ إِنِّي لاَ أَدَعُ بَعْدِي شَيْئًا أَهَمَّ عِنْدِي مِنَ الْكَلاَلَةِ مَا رَاجَعْتُ رَسُولَ اللَّهِ صلى الله عليه وسلم فِي شَىْءٍ مَا رَاجَعْتُهُ فِي الْكَلاَلَةِ وَمَا أَغْلَظَ لِي فِي شَىْءٍ مَا أَغْلَظَ لِي فِيهِ حَتَّى طَعَنَ بِإِصْبَعِهِ فِي صَدْرِي وَقَالَ ‏ "‏ يَا عُمَرُ أَلاَ تَكْفِيكَ آيَةُ الصَّيْفِ الَّتِي فِي آخِرِ سُورَةِ النِّسَاءِ ‏"‏ ‏.‏ وَإِنِّي إِنْ أَعِشْ أَقْضِ فِيهَا بِقَضِيَّةٍ يَقْضِي بِهَا مَنْ يَقْرَأُ الْقُرْآنَ وَمَنْ لاَ يَقْرَأُ الْقُرْآنَ ‏.‏
Reference : Sahih Muslim 1617 a
In-book reference : Book 23, Hadith 11
USC-MSA web (English) reference : Book 11, Hadith 3937
  (deprecated numbering scheme)