Matthew 17:18-20

18And Jesus rebuked him, and the demon came out of him, and the boy was cured 1at once.

19Then the disciples came to Jesus privately and said, “Why could we not drive it out?” 20And He said to them, “Because of the littleness of your faith; for truly I say to you, 2if you have faith 3the size of 4a mustard seed, you will say to 5this mountain, ‘Move from here to there,’ and it will move; and 6nothing will be impossible to you.