صحيح مسلم

Abu Talha reported: 'Umar b. al-Khattab (Allah be pleased with him) delivered a sermon on Friday and made a mention of Allah's Messenger (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.