Matthew 17:10-20

10 Then his disciples asked him, saying, Why then do the scribes say that Elijah must come first?

11 And Jesus answered and said unto them, Elijah truly shall come first and restore all things.

12 But I say unto you, That Elijah is come already, and they knew him not, but have done unto him whatever they pleased. Likewise the Son of man shall also suffer of them.

13 Then the disciples understood that he spoke unto them of John the Baptist.

14 And when they were come to the multitude, there came to him a certain man, kneeling down to him, and saying,

15 Lord, have mercy on my son, for he is lunatic and suffers miserably; for many times he has fallen into the fire and often into the water.

16 And I brought him to thy disciples, and they could not cure him.

17 Then Jesus answered and said, O unfaithful and crooked generation, how long shall I be with you? How long shall I suffer you? Bring him here to me.

18 And Jesus rebuked him, and the demon departed out of him and the child was cured from that very hour.

19 Then the disciples came to Jesus apart and said, Why could not we cast him out?

20 And Jesus said unto them, Because of your unfaithfulness; for verily I say unto you, If ye have faith as a grain of mustard seed, ye shall say unto this mountain, Remove from here to yonder place, and it shall remove; and nothing shall be impossible unto you.