Matthew 17:20 in the King James Version
And Jesus said unto them, Because of your unbelief: for verily I say unto you, If ye have faith as a grain of mustard seed, ye shall say unto this mountain, Remove hence to yonder place; and it shall remove; and nothing shall be impossible unto you.
Context
19 Then the disciples came to Jesus privately, and said, “Why weren’t we able to cast it out?”
20 He said to them, “Because of your unbelief. For most certainly I tell you, if you have faith as a grain of mustard seed, you will tell this mountain, ‘Move from here to there,’ and it will move; and nothing will be impossible for you.
21 But this kind doesn’t go out except by prayer and fasting.”