Romans 8:15-19

For ye have not received the spirit of bondage again to fear; but ye have received the Spirit of adoption, whereby we cry, Abba, Father.

The Spirit itself beareth witness with our spirit, that we are the children of God:

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.

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.

For the earnest expectation of the creature waiteth for the manifestation of the sons of God.