Musnad Abu Ya'la al-Mawsili 65:2

Bishr ibn al-Walid al-Kindi narrated to us, Sahl the brother of Hazm narrated to us, from Abu Imran, from Jundub, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Whoever speaks about the Quran according to his own opinion, and is correct, he has still erred."