Romans 8:16 in the King James Version
The Spirit itself beareth witness with our spirit, that we are the children of God:
Context
15 For you didn’t receive the spirit of bondage again to fear, but you received the Spirit of adoption, by whom we cry, “Abba! Father!”
16 The Spirit himself testifies with our spirit that we are children of God;
17 and if children, then heirs—heirs of God and joint heirs with Christ, if indeed we suffer with him, that we may also be glorified with him.