Matthew 17:18-20

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

19Then the disciples came to Jesus privately and said, “Why couldn’t we cast it out?”

20He told them, “It was because of your little faith. I tell you the truth, if you have faith the size of a mustard seed, you will say to this mountain, ‘Move from here to there,’ and it will move; nothing will be impossible for you.”