Matthew 17:16

Then he said to Gehazi, Gird up thy loins, and take my staff in thine hand, and go thy way: if thou meet any man, salute him not; and if any salute thee, answer him not again: and lay my staff upon the face of the child. And the mother of the child said, As the LORD liveth, and as thy soul liveth, I will not leave thee. And he arose, and followed her. And Gehazi passed on before them, and laid the staff upon the face of the child; but there was neither voice, nor hearing. Wherefore he went again to meet him, and told him, saying, The child is not awaked.

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

And I besought thy disciples to cast him out; and they could not.

And his name through faith in his name hath made this man strong, whom ye see and know: yea, the faith which is by him hath given him this perfect soundness in the presence of you all.

And the evil spirit answered and said, Jesus I know, and Paul I know; but who are ye?