Romans 2:14-16

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

16on the day when God judges what people have kept secret, according to my gospel through Christ Jesus.