Matthew 17:14 (KJV)

And as they came down from the mountain, Jesus charged them, saying, Tell the vision to no man, until the Son of man be risen again from the dead.

And his disciples asked him, saying, Why then say the scribes that Elias must first come?

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

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

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

Lord, have mercy on my son: for he is lunatick, and sore vexed: for ofttimes he falleth into the fire, and oft into the water.

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

Then Jesus answered and said, O faithless and perverse generation, how long shall I be with you? how long shall I suffer you? bring him hither to me.

And Jesus rebuked the devil; and he departed out of him: and the child was cured from that very hour.

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