Doubt visits almost everyone who takes belief seriously. It arrives in the dark hour, in the question you are ashamed to ask aloud, in the gap between what you say and what you feel. The Qur'an does not scold the questioning heart. It answers Ibrahim, who asked to be shown how God gives life, with a gentle has your heart not believed? — and then it shows him.
These verses speak to the one who wants to be sure. Some affirm that the truth has come from your Lord; others trace how certainty grew in the prophets who searched the sky for proof. Read them slowly. They suggest that asking is part of the road home, and that hearts settle when they remember the One they were made for.
2:2 — This is the Book — no doubt is in it — a guidance for those mindful of God,
2:260 — And when Ibrahim said, "My Lord, show me how you give life to the dead," God said, "Do you not believe?" He said, "Yes, but so that my heart may be at peace." God said, "Take four birds and draw them close to yourself, then place a portion of them on each hill, then call them — they will come to you rushing. And know that God is mighty, wise."
6:75 — And so we showed Ibrahim the dominion of the heavens and the earth, that he might be among those who are certain.
10:94 — If you are in doubt about what we have sent down to you, ask those who have been reading the scripture before you. The truth has come to you from your Lord, so do not be among those who waver.
13:28 — those who believe, and whose hearts find peace in the remembrance of God — truly, in the remembrance of God hearts find peace.
41:53 — We will show them our signs on the horizons and within themselves, until it becomes clear to them that this is the truth. Is it not enough that your Lord is witness over all things?
49:15 — The true believers are those who believe in God and his Messenger, then never waver, and who strive with their wealth and their lives in the path of God. They are the truthful ones.
3:7 — It is he who sent down to you the Book. In it are verses precise in meaning — these are the foundation of the Book — and others that are open to multiple readings. Those with deviation in their hearts pursue what is open to multiple readings, seeking discord and seeking to fix its interpretation. But no one knows its interpretation except God. And those firmly grounded in knowledge say, "We believe in it; all of it is from our Lord." Only those with deep understanding take heed.