Musannaf Ibn Abi Shayba 22:14

Jarir narrated to us, from Tha'labah, from Muqatil ibn Hayyan, who said: "The speech of the people of the heaven is Arabic." Then he recited: "Ha-Mim. By the clear Book. Indeed, We have made it an Arabic Qur'an that you might understand. And indeed it is, in the Mother of the Book with Us, surely exalted and full of wisdom."