(9) باب مَا جَاءَ فِي الْمُتَأَوِّلِينَ
'Umar bin Al-Khattab said:
I heard Hisham bin Al-Hakim reciting Surat Al-Furqan during the lifetime of Allah's Messenger (ﷺ). I listened to his recitation and noticed that he recited it in several different ways which Allah's Messenger (ﷺ) had not taught me. So I was about to jump over him during his Salat (prayer) but I waited till he finished his Salat (prayer) whereupon I put, either his upper garment or my upper garment around his neck and seized him by it and asked him, "Who has taught you this Surah?" He replied: "Allah's Messenger (ﷺ) has taught it to me." I said (to him), "You have told a lie! By Allah, Allah's Messenger (ﷺ) has taught me this Surah which I have heard you reciting." So I dragged him to the Allah's Messenger (ﷺ). I said: "O Allah's Messenger I have heard this man reciting Surat Al-Furqan in a way in which you have not taught me, and you did teach me Surah Al-Furqan." On that Allah's Messenger (ﷺ) said, "O 'Umar, release him! Recite, O Hisham". So Hisham recited before him in the way as I heard him reciting. Allah's Messenger (ﷺ) said, "It has been revealed like this." Then Allah's Messenger (ﷺ) said, "Recite, O 'Umar" So recited it. The Prophet (ﷺ) said, "It has been revealed like this." And then he added, "This Qur'an has been revealed to be recited in seven different ways, so recite it whichever way is easier for you."
Reference: Sahih al-Bukhari 6936
In-book reference: Book 88, Hadith 18
USC-MSA web (English) reference(deprecated numbering scheme): Vol. 1, Book 84, Hadith 69