[Matthew 17:19-21] Then the disciples came to Jesus privately and said, “Why could we not cast it out?” So Jesus said to them, “Because of your unbelief; for assuredly, I say to you, if you have faith as a mustard seed, you will say to this mountain, ‘Move from here to there,’ and it will move; and nothing will be impossible for you. However, this kind does not go out except by prayer and fasting.”

[Matthew 21;20-22] And when the disciples saw it, they marveled, saying, “How did the fig tree wither away so soon?” So Jesus answered and said to them, “Assuredly, I say to you, if you have faith and do not doubt, you will not only do what was done to the fig tree, but also if you say to this mountain, ‘Be removed and be cast into the sea,’ it will be done. And whatever things you ask in prayer, believing, you will receive.”