Roman Catechism 31.13

Chapter 31 — Part III: The Decalogue — The Eighth Commandment

Section 13. False Testimony Out Of Court Is Forbidden — Finally, God prohibits all testimony which may inflict injury or injustice, whether it be a matter of legal evidence or not. In the passage of Leviticus where the Commandments are repeated, we read: Thou shalt not steal; thou shalt not lie; neither shall any man deceive his neighbour.' To none, therefore can it be a matter of doubt, that this Commandment condemns lies of every sort, as these words of David explicitly declare: Thou wilt destroy all that speak a lie.