Matthew 17:9-20

And as they were coming down from the mountain, Jesus commanded them, saying, Tell the vision to no man, until the Son of man be risen from the dead. And his disciples asked him, saying, Why then say the scribes that Elijah must first come? And he answered and said, Elijah indeed cometh, and shall restore all things: but I say unto you, that Elijah is come already, and they knew him not, but did unto him whatsoever they would. Even so shall the Son of man also suffer of them. Then understood the disciples that he spake unto them of John the Baptist. And when they were come to the multitude, there came to him a man, kneeling to him, and saying, Lord, have mercy on my son: for he is epileptic, and suffereth grievously; for oft-times he falleth into the fire, and oft-times into the water. And I brought him to thy disciples, and they could not cure him. And Jesus answered and said, O faithless and perverse generation, how long shall I be with you? how long shall I bear with you? bring him hither to me. And Jesus rebuked him; and the demon went out of him: and the boy was cured from that hour. Then came the disciples to Jesus apart, and said, Why could not we cast it out? And he saith unto them, Because of your little faith: for verily I say unto you, If ye have faith as a grain of mustard seed, ye shall say unto this mountain, Remove hence to yonder place; and it shall remove; and nothing shall be impossible unto you.