Romans 2:14.

King James Bible
For when the Gentiles, which have not the law, do by nature the things contained in the law, these, having not the law, are a law unto themselves: Romans 2:14.
When I was fighting not to become a Christian in my flat in The Barrio Pilar, Madrid, back at Easter 1973 this verse answered my last argument.
I read it unsaved and several seconds later I embraced the Living Jesus as my Lord and Personal Saviour.