Musnad Ahmad 188:0

Hisham ibn Hakim ibn Hizam said: I heard Hisham ibn Hakim ibn Hizam reciting Surat al-Furqan during the lifetime of the Messenger of Allah (ﷺ). I listened to his recitation, and behold, he was reciting it in many different ways that the Messenger of Allah (ﷺ) had not taught me. I was about to pounce on him while he was praying, but I waited until he finished his prayer. Then I grabbed him by his garment and brought him to the Messenger of Allah (ﷺ). I said: "O Messenger of Allah, I heard this man reciting Surat al-Furqan in a way that you did not teach me." The Messenger of Allah (ﷺ) said to him: "Recite." So he recited it in the way I had heard him. The Messenger of Allah (ﷺ) said: "Thus it was revealed." Then he said to me: "Recite." So I recited it in the way he had taught me. The Messenger of Allah (ﷺ) said: "Thus it was revealed. Indeed, this Quran was revealed in seven ahruf (modes/dialects), so recite from it what is easy for you."