Romans 2:13-15

13For the hearers of the law are not righteous before God, but the doers of the law will be justified.

14So, when Gentiles, who do not by nature have the law, do what the law demands, they are a law to themselves even though they do not have the law.

15They show that the work of the law is written on their hearts. Their consciences confirm this. Their competing thoughts either accuse or even excuse them