Musnad Abu Ya'la al-Mawsili 3:299

Ubayd Allah narrated to us, Abd al-Rahman narrated to us, Shu'bah narrated to us, from 'Awn ibn Abi Juhayfah, from his father, who said: Ali said: "If I narrate to you from the Messenger of Allah (may Allah bless him and grant him peace), then for me to fall from the sky is more beloved to me than to say about the Messenger of Allah (may Allah bless him and grant him peace) what he did not say. But war is deception."