Matthew 17:19-21

Mace(i) 19 then came the disciples to Jesus in private, and said, why could not we cast him out? 20 because of your incredulity, said Jesus: for I tell you truly, if ye had ever so little faith, ye might say to this mountain, remove hence to yonder place, and it should remove; and nothing would be too difficult for you. 21 however, such a distemper is not to be removed but by prayer and fasting.