Scripture is explicit

Is it a sin to question God?

Q: Is it a sin to doubt God exists?

No passage treats the question as an offence. Scripture records the doubt of prophets and apostles without condemning it, and the man in Mark 9:24 who says 'I believe; help my unbelief' is answered rather than corrected.

The Bible is full of people who did

An open scroll of psalms lit by one candle at night, beneath a wide dark window.

In short

No. Scripture records question after question put to God, and none of them is rebuked as sin. Job demands an answer, the psalms ask how long, Habakkuk accuses God of ignoring violence. All three are in the Bible because they were kept, not despite being kept.

What the text says

Psalms 13:1

[To the chief Musician, A Psalm of David.] How long wilt thou forget me, O LORD? for ever? how long wilt thou hide thy face from me? chief...: or, overseer

David says this to God, not about him, and it is in the songbook of the temple. A complaint this direct was put in the hymnal, which tells you what the tradition thought of the question.

Habakkuk 1:2 was the verse of the day on July 30, 2022. See that day

Often brought inHabakkuk 1:2

O LORD, how long shall I cry, and thou wilt not hear! even cry out unto thee of violence, and thou wilt not save!

A prophet accusing God of inaction. The book that follows is God's answer, not his rebuke.

The counterweightJohn 20:27

Then saith he to Thomas, Reach hither thy finger, and behold my hands; and reach hither thy hand, and thrust it into my side: and be not faithless, but believing.

Often read as a reproach. Notice what precedes it: the demand is met before the words are spoken.