Musannaf Ibn Abi Shayba 22:192

Ali ibn Mushir narrated to us, from al-Hasan ibn Amr, from al-Sha’bi, who said: I reached the companions of Abdullah and the companions of Ali, and there was nothing of knowledge they disliked more than the interpretation of the Quran. He said: And Abu Bakr used to say, "Which sky would shade me and which earth would carry me if I were to say about the Book of Allah that which I do not know?"