Musannaf Ibn Abi Shayba 17:897

Abu Bakr narrated to us, he said: Shareek narrated to us, from Ibn ‘Awn, from Ibn Sirin, who said: It reached ‘Umar that a man was telling stories in Basra. So he wrote to him: "Alif-Lam-Ra. These are the verses of the clear Book. Indeed, We have sent it down as an Arabic Qur’an that you might understand. We relate to you, [O Muhammad], the best of stories." He said: So the man recognized [the intent of the message] and stopped.