Do not entertain impure thoughts!

The LORD saw how great man's wickedness on the earth had become, and that every inclination of the thoughts of his heart was only evil all the time. Genesis 6:5

Let the wicked forsake his way and the evil man his thoughts. Let him turn to the LORD, and he will have mercy on him, and to our God, for he will freely pardon. Isaiah 55:7

Have you not discriminated among yourselves and become judges with evil thoughts? James 2:4

For from within, out of men's hearts, come evil thoughts, sexual immorality, theft, murder, adultery. Mark 7:21

Knowing their thoughts, Jesus said, "Why do you entertain evil thoughts in your hearts? Matthew 9:4

Their feet rush into sin; they are swift to shed innocent blood. Their thoughts are evil thoughts; ruin and destruction mark their ways. Isaiah 59:7

What causes fights and quarrels among you? Don't they come from your desires that battle within you? James 4:1

O Jerusalem, wash the evil from your heart and be saved. How long will you harbor wicked thoughts? Jeremiah 4:14

Blind Pharisee! First clean the inside of the cup and dish, and then the outside also will be clean Matthew 23:26.
Clothe yourselves with the Lord Jesus Christ, and do not think about how to gratify the desires of the sinful nature Romans 13:14

Those who live according to the sinful nature have their minds set on what that nature desires; but those who live in accordance with the Spirit have their minds set on what the Spirit desires Romans 8:5.

We all stumble in many ways. If anyone is never at fault in what he says, he is a perfect man, able to keep his whole body in check James 3:2.

Don’t let anyone look down on you because you are young, but set an example for the believers in speech, in life, in love, in faith and in purity. 1 Timothy 4:12

But among you there must not be even a hint of sexual immorality, or of any kind of impurity, or of greed, because these are improper for God’s holy people. Ephesians 5:3

It is God's will that you should be sanctified: that you should avoid sexual immorality; that each of you should learn to control his own body in a way that is holy and honorable, 5 not in passionate lust like the heathen, who do not know God. 1 Thess. 4:3-5
Do not commit adultery.' But I tell you that anyone who looks at a woman lustfully has already committed adultery with her in his heart. Matthew 5:27-30

Flee the evil desires of youth, and pursue righteousness, faith, love and peace, along with those who call on the Lord out of a pure heart. 2 Timothy 2:22

Be self-controlled and alert. Your enemy the devil prowls around like a roaring lion looking for someone to devour. 1 Peter 5:8

How can a young man keep his way pure? By living according to your word. Psalm 119:9

Treat younger men as brothers, 2 older women as mothers, and younger women as sisters, with absolute purity. 1 Timothy 5:1-2

Finally, brothers, whatever is true, whatever is noble, whatever is right, whatever is pure, whatever is lovely, whatever is admirable--if anything is excellent or praiseworthy--think about such things. Philippians 4:8

For everything in the world--the cravings of sinful man, the lust of his eyes and the boasting of what he has and does--comes not from the Father but from the world. The world and its desires pass away, but the man who does the will of God lives forever. 1 John 2:16,17

You will have these tassels to look at and so you will remember all the commands of the LORD, that you may obey them and not prostitute yourselves by going after the lusts of your own hearts and eyes. Numbers 15:39