1 Thessalonians 4:3, 6
1 Thessalonians 4:3 AMP
For this is the will of God, that you be sanctified [separated and set apart from sin]: that you abstain and back away from sexual immorality
1 Thessalonians 4:6 AMP
and that [in this matter of sexual misconduct] no man shall transgress and defraud his brother because the Lord is the avenger in all these things, just as we have told you before and solemnly warned you.