What is the sixth commandment of God? The sixth commandment of God is: Thou shalt not commit adultery.
Thou shalt not commit adultery. (Exodus 20:14)
What are we commanded by the sixth commandment? By the sixth commandment we are commanded to be pure and modest in our behavior.
I exhort you therefore, brethren, by the mercy of God, to present your bodies as a sacrifice, living, holy, pleasing to God. (Romans 12:1)
What does the sixth commandment forbid? The sixth commandment forbids all impurity and immodesty in words, looks, and actions, whether alone or with others.
But immorality and every uncleanness or covetousness, let it not even be named among you, as becomes saints. (Ephesians 5:3)
More on that here -> CCC 2231-2236