Galatians 2:20 says: I am crucified with Christ: nevertheless I live; yet not I, but Christ liveth in me: and the life which I now live in the flesh I live by the faith of the Son of God, who loved me, and gave himself for me.
(KJV).
The verse appears in Galatians 2, in Paul's account of confronting Peter at Antioch. Read it in context at Galatians 2:20, or the full chapter at Galatians 2.