What is the eighth commandment of God? The eighth commandment of God is: Thou shalt not bear false witness against thy neighbor.
Thou shalt not bear false witness against thy neighbor. (Exodus 20:16)
What are we commanded by the eighth commandment? By the eighth commandment we are commanded to speak the truth in all things, but especially in what concerns the good name and honor of others.
Wherefore, put away lying and speak truth each one with his neighbor, because we are members of one another. (Ephesians 4:25)
What does the eighth commandment forbid? The eighth commandment forbids lies, rash judgment, detraction, calumny, and the telling of secrets we are bound to keep.
Lying lips are an abomination to the Lord. (Proverbs 12:22)
More on that here -> CCC 2464-2474