'Doubts' in the Bible

Then he said to them, "Why are you frightened, and why do doubts arise in your hearts?

But the man who doubts is condemned if he eats, because he does not do so from faith, and whatever is not from faith is sin.

But he must ask in faith without doubting, for the one who doubts is like a wave of the sea, blown and tossed around by the wind.