What does the Bible say about doubt?

Immediately the boy’s father cried out, “I do believe; help my unbelief!”Mark 9:24

I believe; help my unbelief. Said by a father in the middle of asking, and the request is granted.

Then Jesus said to Thomas, “Put your finger here and look at My hands. Reach out your hand and put it into My side. Stop doubting and believe.”John 20:27

Thomas is not rebuked for wanting evidence; he is given it.

For the choirmaster. A Psalm of David. How long, O LORD? Will You forget me forever? How long will You hide Your face from me?Psalms 13:1

How long, LORD — four times in two verses, addressed to the one apparently absent.

How long, O LORD, must I call for help but You do not hear, or cry out to You, “Violence!” but You do not save?Habakkuk 1:2

A prophet opens his book by complaining that God is not listening.

to ask Him, “Are You the One who was to come, or should we look for someone else?”Matthew 11:3

John the Baptist, in prison, sends to ask whether he was right about Jesus.

And indeed, have mercy on those who doubt;Jude 1:22

Be merciful to those who doubt — instruction about how to treat them.