Matthew 17:18-20

18Then Jesus rebuked the demon in the boy, and it left him. From that moment the boy was well.

19Afterward the disciples asked Jesus privately, “Why couldn’t we cast out that demon?”

20“You don’t have enough faith,” Jesus told them. “I tell you the truth, if you had faith even as small as a mustard seed, you could say to this mountain, ‘Move from here to there,’ and it would move. Nothing would be impossible.”