Matthew 17:19-21

Thomson(i) 19 Then the disciples came to Jesus in private, and said, Why could not we cast it out? 20 And Jesus said to them, Because of your unbelief. For verily I say to you, If you have faith as a grain of mustard seed, you might say to that mountain, Remove hence to yonder place; and it would remove; and nothing would be impossible to you: 21 but this kind [of power] goeth not forth, unless by prayer and fasting.