Matthew 17:18-20

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

19Afterward the disciples came to Jesus privately and asked, “Why couldn’t we drive it out?”

20“Because you have so little faith,” He answered. “For truly I tell you, if you have faith 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.”1