Romans 8:16-18 The Spirit (o. pneuma) itself bears witness with our spirit, (o. pneuma) that we are the children of God:

UKJV⁽ⁱ⁾ ¹⁶ The Spirit (o. pneuma) itself bears witness with our spirit, (o. pneuma) that we are the children of God: ¹⁷ And if children, then heirs; heirs of God, and joint-heirs with Christ; if so be that we suffer with him, that we may be also glorified together. ¹⁸ For I reckon that the sufferings of this present time are not worthy to be compared with the glory which shall be revealed in us.