Matthew 17:19-21

Young's Literal Translation

¹⁹ Then the disciples having come to Jesus by himself, said, `Wherefore were we not able to cast him out?'

²⁰ And Jesus said to them, `Through your want of faith; for verily I say to you, if ye may have faith as a grain of mustard, ye shall say to this mount, Remove hence to yonder place, and it shall remove, and nothing shall be impossible to you,

²¹ and this kind doth not go forth except in prayer and fasting.'