Romans 2:14-15

When Gentiles, who do not have the Law [since it was given only to Jews], do instinctively the things the Law requires [guided only by their conscience], they are a law to themselves, though they do not have the Law. They show that the essential requirements of the Law are written in their hearts; and their conscience [their sense of right and wrong, their moral choices] bearing witness and their thoughts alternately accusing or perhaps defending them