1 John 4:2

2 This is how you can recognize the Spirit of God: Every spirit that acknowledges that Jesus Christ has come in the flesh is from God,

Read 1 John 4:2 Using Other Translations

Hereby know ye the Spirit of God: Every spirit that confesseth that Jesus Christ is come in the flesh is of God:
By this you know the Spirit of God: every spirit that confesses that Jesus Christ has come in the flesh is from God,
This is how we know if they have the Spirit of God: If a person claiming to be a prophet acknowledges that Jesus Christ came in a real body, that person has the Spirit of God.