Matthew 17:10-20

10 His disciples asked him, saying, "Then why do the scribes say that Elijah must come first?

11 Jesus answered them, "Elijah indeed comes first, and will restore all things,

12 but I tell you that Elijah has come already, and they didn't recognize him, but did to him whatever they wanted to. Even so will the Son of Man also suffer by them."

13 Then the disciples understood that he spoke to them of John the Baptizer.

14 When they came to the multitude, there came to him a man, kneeling to him, saying,

15 "Lord, have mercy on my son, for he is epileptic, and suffers grievously; for he often falls into the fire, and often into the water.

16 So I brought him to your disciples, and they could not cure him."

17 Jesus answered, "Faithless and perverse generation! How long will I be with you? How long will I bear with you? Bring him here to me."

18 Jesus rebuked him, the demon went out of him, and the boy was cured from that hour.

19 Then the disciples came to Jesus privately, and said, "Why were we not able to cast it out?"

20 He said to them, "Because of your unbelief. For most assuredly I tell you, if you have faith as a grain of mustard seed, you will tell this mountain, 'Move from here to there,' and it will move; and nothing will be impossible to you.