Matthew 17:18-20

18Jesus ordered the demon to come out of the boy. At that moment the boy was cured.

19Then the disciples came to Jesus privately and asked, “Why couldn’t we force the demon out of the boy?”

20He told them, “Because you have so little faith. I can guarantee this truth: If your faith is the size of a mustard seed, you can say to this mountain, ‘Move from here to there,’ and it will move. Nothing will be impossible for you.”