Genesis 4:7
God tells Cain that if he does what is right he will be accepted. Also, that sin desires Cain, but Cain should rule over it. Just like we are told in the New Testament to not be the servants of sin and that we are to resist the devil and he will flee from us. However, it does not say that he will stay away. Resisting the devil is a continuous process, and we must not let our guard down.