'Doubt' in the Bible

Immediately Jesus stretched out His hand and took hold of him, and *said to him, “You of little faith, why did you doubt?”

And Jesus answered and said to them, “Truly 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 even if you say to this mountain, ‘Be taken up and cast into the sea,’ it will happen.