The utterances of truth we judge by no separate test, giving full credit to itself.  And God, the Father of the universe, who is the perfect intelligence, is the truth.  And the Word, being His Son, came to us, having put on flesh, revealing both Himself and the Father, giving to us in Himself resurrection from the dead, and eternal life afterwards.  And this is Jesus Christ, our Savior and Lord.  He, therefore, is Himself both the faith and the proof of Himself and of all things.  Wherefore those who follow Him, and know Him, having faith in Him as their proof, shall rest in Him.

-- Justin Martyr, On the Resurrection