Matthew 17:17-20

And Jesus answered and said, “You unbelieving and perverted generation, how long shall I be with you? How long shall I put up with you? Bring him here to Me.” And Jesus rebuked him, and the demon came out of him, and the boy was cured at once. Then the disciples came to Jesus privately and said, “Why could we not drive it out?” And He *said to them, “Because of the littleness of your faith; for truly I say to you, 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; and nothing will be impossible to you.