Sahih Muslim 820a

Ubayy b. Ka'b reported:I was in the mosque when a man entered and prayed and recited (the Qur'in) in a style to which I objected. Then another man entered (the mosque) and recited in a style different from that of his companion. When we had finished the prayer, we all went to Allah's Messenger (ﷺ) and said to him: This man recited in a style to which I objected, and the other entered and recited in a style different from that of his companion. The Messenger of Allah (ﷺ) asked them to recite and so they recited, and the Messenger of Allah (ﷺ) expressed approval of their affairs (their modes of recitation). and there occurred In my mind a sort of denial which did not occur even during the Days of Ignorance. When the Messenger of Allah (ﷺ) saw how I was affected (by a wrong idea), he struck my chest, whereupon I broke into sweating and felt as though I were looking at Allah with fear. He (the Holy Prophet) said to me: Ubayy. a message was sent to me to recite the Qur'an in one dialect, and I replied: Make (things) easy for my people. It was conveyed to me for the second time that it should be recited in two dialects. I again replied to him: Make affairs easy for my people. It was again conveyed to me for the third time to recite in seven dialects And (I was further told): You have got a seeking for every reply that I sent you, which you should seek from Me. I said: O Allah! forgive my people, forgive my people, and I have deferred the third one for the day on which the entire creation will turn to me, including even Ibrahim (peace be upon him) (for intercession)