Musnad Ahmad 2:26

Abu al-Mughirah narrated to us, Safwan narrated to us, Shurayh ibn Ubayd narrated to us, he said: Umar ibn al-Khattab said: I went out to encounter the Messenger of Allah (may Allah bless him and grant him peace) before I accepted Islam. I found that he had preceded me to the mosque, so I stood behind him. He began reciting Surat al-Haqqah, and I began to marvel at the composition of the Quran. He said: I said, "By Allah, this is a poet, just as Quraysh said." He said: Then he recited: "That it is the word of a noble Messenger. And it is not the word of a poet; little do you believe." He said: I said, "A soothsayer." He said: "Nor the word of a soothsayer; little do you remember. [It is] a revelation from the Lord of the worlds. And if he had made up about Us some [false] sayings, We would have seized him by the right hand; then We would have cut from him the aorta. And there is no one of you who could prevent [Us] from him," until the end of the surah. He said: Then Islam settled into my heart in every place.