Every mention of unbelief I can find:
Romans 3:1-6
>What advantage then has the Jew, or what is the profit of circumcision? Much in every way! Chiefly because to them were committed the oracles of God. For what if some did not believe? Will their unbelief make the faithfulness of God without effect? Certainly not! Indeed, let God be true but every man a liar. As it is written: “That You may be justified in Your words, and may overcome when You are judged.” But if our unrighteousness demonstrates the righteousness of God, what shall we say? Is God unjust who inflicts wrath? (I speak as a man.) Certainly not! For then how will God judge the world?
Romans 4:16-22
>Therefore it is of faith that it might be according to grace, so that the promise might be sure to all the seed, not only to those who are of the law, but also to those who are of the faith of Abraham, who is the father of us all (as it is written, “I have made you a father of many nations”) in the presence of Him whom he believed—God, who gives life to the dead and calls those things which do not exist as though they did; who, contrary to hope, in hope believed, so that he became the father of many nations, according to what was spoken, “So shall your descendants be.” And not being weak in faith, he did not consider his own body, already dead (since he was about a hundred years old), and the deadness of Sarah’s womb. He did not waver at the promise of God through unbelief, but was strengthened in faith, giving glory to God, and being fully convinced that what He had promised He was also able to perform. And therefore “it was accounted to him for righteousness.”
Romans 11:19-24
>You will say then, “Branches were broken off that I might be grafted in.” Well said. Because of unbelief they were broken off, and you stand by faith. Do not be haughty, but fear. For if God did not spare the natural branches, He may not spare you either. Therefore consider the goodness and severity of God: on those who fell, severity; but toward you, goodness, if you continue in His goodness. Otherwise you also will be cut off. And they also, if they do not continue in unbelief, will be grafted in, for God is able to graft them in again. For if you were cut out of the olive tree which is wild by nature, and were grafted contrary to nature into a cultivated olive tree, how much more will these, who are natural branches, be grafted into their own olive tree?
1 Corinthians 6:1-6
>Dare any of you, having a matter against another, go to law before the unrighteous, and not before the saints? Do you not know that the saints will judge the world? And if the world will be judged by you, are you unworthy to judge the smallest matters? Do you not know that we shall judge angels? How much more, things that pertain to this life? If then you have judgments concerning things pertaining to this life, do you appoint those who are least esteemed by the church to judge? I say this to your shame. Is it so, that there is not a wise man among you, not even one, who will be able to judge between his brethren? But brother goes to law against brother, and that before unbelievers!
1 Corinthians 7:12-16
>But to the rest I, not the Lord, say: If any brother has a wife who does not believe, and she is willing to live with him, let him not divorce her. And a woman who has a husband who does not believe, if he is willing to live with her, let her not divorce him. For the unbelieving husband is sanctified by the wife, and the unbelieving wife is sanctified by the husband; otherwise your children would be unclean, but now they are holy. But if the unbeliever departs, let him depart; a brother or a sister is not under bondage in such cases. But God has called us to peace. For how do you know, O wife, whether you will save your husband? Or how do you know, O husband, whether you will save your wife?
1 Corinthians 14:22-25
>Therefore tongues are for a sign, not to those who believe but to unbelievers; but prophesying is not for unbelievers but for those who believe. Therefore if the whole church comes together in one place, and all speak with tongues, and there come in those who are uninformed or unbelievers, will they not say that you are out of your mind? But if all prophesy, and an unbeliever or an uninformed person comes in, he is convinced by all, he is convicted by all. And thus the secrets of his heart are revealed; and so, falling down on his face, he will worship God and report that God is truly among you.