When Jesus saw that the people came running together,....hytwl, "to him", as the Syriac version adds, and so the Persic; upon hearing the vehement cry of the father of the child, and the earnest solicitations he made, expecting that something would be done:he rebuked the foul spirit; that brought this disorder on the child, had continued it so long, and with so much violence.
Matthew calls this foul spirit, "the devil", See Gill on "Mt 17:18":saying unto him, thou dumb and deaf spirit; so calling him, not because the spirit was dumb and deaf, but because he had been the cause of dumbness and deafness in the child: he had at times taken away both his speech and hearing:I charge thee come out of him, and enter no more into him.
Christ, in an authoritative way, ordered the unclean spirit to leave his possession, and never attempt to regain it more.