Mattityahu 17:14-20

And when they came to the multitude, a man came up to Rebbe, Melech HaMoshiach, falling down before him. And the man said, Adoni, grant rachamim (mercy) on this ben (son) of mine, for he is an epileptic, and suffers horribly; for often he falls into the eish, and often into the mayim. And I brought him to your talmidim, and they could not give him refuah. And Rebbe, Melech HaMoshiach said in reply, O perverted generation without emunah, how long shall I be with you? How long shall I put up with you? Bring him here to me. And Rebbe, Melech HaMoshiach rebuked it, and the shed came out of him, and the bocher received his refuah that hour. Then the talmidim came to Rebbe, Melech HaMoshiach in a yechidus (private meeting with the Rebbe), and said, Why were we not able to cast it out? And Rebbe, Melech HaMoshiach said to them, On account of your little emunah, for, omein, I say to you, if you have emunah as a mustard seed, you shall say to this mountain, Move from here, and it shall be moved; and nothing shall be impossible for you.