Whether or not they know it they are bearing witness to the law... even if they don't understand that it applies to them as well (looking at a man / woman with lust = adultery). (redeeminggod.com)
For example, adultery was a sin punishable by death, but Jesus told the people if you look at a woman with lust in your heart you have committed adultery. (religion.blogs.cnn.com)
Or again, Jesus taught, «Everyone who looks at a women with lust has already committed adultery with her in his heart» (Matthew 5:28). (religion.blogs.cnn.com)