Musnad Ahmad 5:563

'Abd al-Rahman ibn Mahdi and Muhammad ibn Ja'far narrated to us, they said: Shu'bah narrated to us, from 'Awn ibn Abi Juhayfah, from his father, who said: Ali said: "If I narrate to you a hadith from the Messenger of Allah, may Allah bless him and grant him peace, then for me to fall from the sky to the earth is more beloved to me than that I should say about the Messenger of Allah, may Allah bless him and grant him peace, that which he did not say. But war is deception."