'Doubt' in the Bible

Immediately Jesus extended His hand and caught him, saying to him, “O you of little faith, why did you doubt?”

Jesus replied to them, “I assure you and most solemnly say to you, if you have faith [personal trust and confidence in Me] and do not doubt or allow yourself to be drawn in two directions, you will not only do what was done to the fig tree, but even if you say to this mountain, ‘Be taken up and thrown into the sea,’ it will happen [if God wills it].