Matthew 17:21 (KJV)

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?

And Jesus said unto them, Because of your unbelief: 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.

And while they abode in Galilee, Jesus said unto them, The Son of man shall be betrayed into the hands of men:

And they shall kill him, and the third day he shall be raised again. And they were exceeding sorry.

And when they were come to Capernaum, they that received tribute money came to Peter, and said, Doth not your master pay tribute?

He saith, Yes. And when he was come into the house, Jesus prevented him, saying, What thinkest thou, Simon? of whom do the kings of the earth take custom or tribute? of their own children, or of strangers?

Peter saith unto him, Of strangers. Jesus saith unto him, Then are the children free.