'Have Faith' in the Bible

And he said to them, Because of your want of faith. For truly do I say to you, If ye have faith as a grain of mustard, ye shall say to this mountain, Remove hence to yonder place, and it will remove; and nothing will be impossible to you.

Jesus answering said to them, Truly do I say to you, If ye have faith, and do not doubt, not only shall ye do what hath been done to the figtree, but should ye even say to this mountain, Be thou taken up and cast into the sea, it would be done.