Romans 2:14, 15

New International Version (NIV)

¹⁴ (Indeed, when Gentiles, who do not have the law, do by nature things required by the law,(A) they are a law for themselves, even though they do not have the law. ¹⁵ They show that the requirements of the law are written on their hearts, their consciences also bearing witness, and their thoughts sometimes accusing them and at other times even defending them.)

From BibleGateway.com: http://www.biblegateway.com/passage/?search=Romans 2:14-15&version=NIV
NIV®