Matthew 5:28

but I tell you, that whosoever looketh on a woman, so as to lust after her, hath already debauched her in his heart.

Matthew 12:35

A good man out of the good treasure of the heart produceth good things; and a wicked man out of the wicked treasure uttereth wicked things:

Matthew 15:19

For out of the heart proceed wicked disputings, murders, adulteries, fornications, thefts, false-witnessings, slanders:

Treasury of Scripture Knowledge

Summary

And let none of you imagine evil in your hearts against his neighbour; and love no false oath: for all these are things that I hate, saith the LORD.

Bible References

Let

Matthew 5:28
but I tell you, that whosoever looketh on a woman, so as to lust after her, hath already debauched her in his heart.
Matthew 12:35
A good man out of the good treasure of the heart produceth good things; and a wicked man out of the wicked treasure uttereth wicked things:
Matthew 15:19
For out of the heart proceed wicked disputings, murders, adulteries, fornications, thefts, false-witnessings, slanders: