Musnad Ahmad 26:431

Yahya ibn Adam narrated to us, Abu Bakr narrated to us, from Asim ibn Abi al-Najud, from Zirr ibn Hubaysh, from Abdullah ibn Mas’ud, who said: The Messenger of Allah, may Allah bless him and grant him peace, taught me to recite a surah from the "Thalathin" (the thirties), from the "Ha-Mim" [surahs]. He said: Meaning al-Ahqaf. He said: And the surah, when it was more than thirty verses, was called "the thirties." He said: So I went to the mosque, and there was a man reciting it differently than how he had taught me. I said: "Who taught you to recite it?" He said: "The Messenger of Allah, may Allah bless him and grant him peace." He said: So I said to another: "Recite it," and he recited it differently than my recitation and the recitation of my companion. So I took them both to the Prophet, may Allah bless him and grant him peace, and I said: "O Messenger of Allah, these two are differing with me in the recitation!" He said: So he became angry, and his face changed color, and he said: "Indeed, those who were before you were only destroyed by disagreement." Zirr said: And there was a man with him. He said: So the man said: "Indeed, the Messenger of Allah, may Allah bless him and grant him peace, commands you that each man among you should recite as he was taught, for indeed, those who were before you were only destroyed by disagreement." Abdullah said: "I do not know if it was something the Messenger of Allah, may Allah bless him and grant him peace, whispered to him, or if he knew what was in the soul of the Messenger of Allah, may Allah bless him and grant him peace." He said: "And the man was Ali ibn Abi Talib, may the prayers of Allah be upon him."