Romans 10:9 That if thou shalt confess with thy mouth the Lord Jesus, and shalt believe in thine heart that God hath raised him from the dead, thou shalt be saved.
I was saved when I fulfilled both parts of Romans 10, verse 9. Since I evidenced the power of the holy spirit as the men in Acts 19:6 did, I know I've received salvation as intended.
Romans 8:16,17 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...