Matthew 5:28

But I say to you that everyone who looks at a woman with lustful intent has already committed adultery with her in his heart.

Proverbs 6:25

Do not lust in your heart after her beauty or let her captivate you with her eyes,

Matthew 15:19

For out of the heart come evil thoughts, murder, adultery, sexual immorality, theft, false testimony, slander.

James 1:15

Then, after desire has conceived, it gives birth to sin; and sin, when it is full-grown, gives birth to death.