Romans 2:14-15

For example, whenever people who don’t possess the law as their birthright commit sin, it still confirms that a “law” is present in their conscience. For when they instinctively do what the law requires, that becomes a “law” to govern them, even though they don’t have Mosaic law. It demonstrates that the requirements of the law are woven into their hearts. They know what is right and wrong, for their conscience validates this “law” in their heart. Their thoughts correct them in one instance and commend them in another.