From the Heidelberg Catechism for the Lord’s Day, October 27

Ninth Commandment

“You shall not bear false witness against your neighbor.”

112. What does the ninth Commandment require?
That I bear false witness against no one, twist no one’s words, be no backbiter or slanderer, join in condemning no one unheard or rashly; but that on pain of God’s heavy wrath, I avoid all lying and deceit as the very works of the devil; and that in matters of judgment and justice and in all other affairs, I love, speak honestly, and confess the truth; also, insofar as I can, defend and promote my neighbor’s good name.