Mark 9:27

When Jesus saw that the people came running together, he rebuked the foul spirit, saying unto him, Thou dumb and deaf spirit, I charge thee, come out of him, and enter no more into him.

And the spirit cried, and rent him sore, and came out of him: and he was as one dead; insomuch that many said, He is dead.

And when he was come into the house, his disciples asked him privately, Why could not we cast him out?

And he said unto them, This kind can come forth by nothing, but by prayer and fasting.