Mark 9:25-29

And when Jesus saw that a multitude came running together, he rebuked the unclean spirit, saying unto him, Thou dumb and deaf spirit, I command thee, come out of him, and enter no more into him. And having cried out, and torn him much, he came out: and the boy became as one dead; insomuch that the more part said, He is dead. But Jesus took him by the hand, and raised him up; and he arose. And when he was come into the house, his disciples asked him privately, How is it that we could not cast it out? And he said unto them, This kind can come out by nothing, save by prayer.