Matthew 17:18-20

18Jesus said to the bad spirit, ‘Stop!’ Then the bad spirit left the boy and immediately he became well again.

19When the disciples were alone with Jesus, they asked him, ‘Why could we not make the bad spirit leave the boy?’

20Jesus replied, ‘You could not do it because you do not trust God very much. I tell you this: You may believe in God only a little bit, like a very small seed. Even then, you could say to this mountain, “Go away from this place and move to that other place.” Then it will move. Nothing will be impossible for you to do.’ [