Matthew 17:18-20

18Jesus rebuked the demon, and it came out of the boy, and he was healed at that moment.

19Then the disciples came to Jesus in private and asked, “Why couldn’t we drive it out?” 20He replied, “Because you have so little faith. Truly I tell you, if you have faith as small as a mustard seed, you can say to this mountain, ‘Move from here to there,’ and it will move. Nothing will be impossible for you.”