2 Corinthians 5:17 says: Therefore if any man be in Christ, he is a new creature: old things are passed away; behold, all things are become new.
(KJV).
The verse appears in 2 Corinthians 5, a chapter that describes reconciliation to God through Christ. Read it in context at 2 Corinthians 5:17, or the full chapter at 2 Corinthians 5.