Sura al-Tawbah 9:45

إِنَّمَا يَسْتَـْٔذِنُكَ ٱلَّذِينَ لَا يُؤْمِنُونَ بِٱللَّـهِ وَٱلْيَوْمِ ٱلْأَخِرِ وَٱرْتَابَتْ قُلُوبُهُمْ فَهُمْ فِى رَيْبِهِمْ يَتَرَدَّدُونَ

innamā yastaʾdhinuka lladhīna lā yuʾminūna billāhi wa-l-yawmi l-akhiri wa-irtābat qulūbuhum fa-hum fī raybihim yataraddadūna

Only those ask thee for exemption who believe not in Allah and the Last Day, and whose hearts are in doubt, so that they are tossed in their doubts to and fro.

Sura al-Nūr 24:50

أَفِى قُلُوبِهِم مَّرَضٌ أَمِ ٱرْتَابُوٓا۟ أَمْ يَخَافُونَ أَن يَحِيفَ ٱللَّـهُ عَلَيْهِمْ وَرَسُولُهُۥ بَلْ أُو۟لَٰٓئِكَ هُمُ ٱلظَّٰلِمُونَ

afī qulūbihim maraḍun ami irtābū am yakhāfūna an yaḥīfa allāhu ʿalayhim wa-rasūluhu bal ulāʾika humu l-ẓālimūna

Is it that there is a disease in their hearts? or do they doubt, or are they in fear, that Allah and His Messenger will deal unjustly with them? Nay, it is they themselves who do wrong.

Sura al-ʿAnkabūt 29:48

وَمَا كُنتَ تَتْلُوا۟ مِن قَبْلِهِۦ مِن كِتَٰبٍ وَلَا تَخُطُّهُۥ بِيَمِينِكَ إِذًا لَّٱرْتَابَ ٱلْمُبْطِلُونَ

wa-mā kunta tatlū min qablihi min kitābin wa-lā ṭakhuṭṭuhu bi-yamīnika idhan la-irtāba l-mubṭilūna

And thou wast not (able) to recite a Book before this (Book came), nor art thou (able) to transcribe it with thy right hand: In that case, indeed, would the talkers of vanities have doubted.

Sura al-Ḥujurāt 49:15

إِنَّمَا ٱلْمُؤْمِنُونَ ٱلَّذِينَ ءَامَنُوا۟ بِٱللَّـهِ وَرَسُولِهِۦ ثُمَّ لَمْ يَرْتَابُوا۟ وَجَٰهَدُوا۟ بِأَمْوَٰلِهِمْ وَأَنفُسِهِمْ فِى سَبِيلِ ٱللَّـهِ أُو۟لَٰٓئِكَ هُمُ ٱلصَّٰدِقُونَ

innamā l-muʾminūna lladhīna āmanū billāhi wa-rasūlihi thumma lam yartābū wa-jāhadū bi-amwālihim wa-anfusihim fī sabīli allāhi ulāʾika humu l-ṣādiqūna

Only those are Believers who have believed in Allah and His Messenger, and have never since doubted, but have striven with their belongings and their persons in the Cause of Allah: Such are the sincere ones.

Sura al-Muddaththir 74:31

وَمَا جَعَلْنَآ أَصْحَٰبَ ٱلنَّارِ إِلَّا مَلَٰٓئِكَةً وَمَا جَعَلْنَا عِدَّتَهُمْ إِلَّا فِتْنَةً لِّلَّذِينَ كَفَرُوا۟ لِيَسْتَيْقِنَ ٱلَّذِينَ أُوتُوا۟ ٱلْكِتَٰبَ وَيَزْدَادَ ٱلَّذِينَ ءَامَنُوٓا۟ إِيمَٰنًا وَلَا يَرْتَابَ ٱلَّذِينَ أُوتُوا۟ ٱلْكِتَٰبَ وَٱلْمُؤْمِنُونَ وَلِيَقُولَ ٱلَّذِينَ فِى قُلُوبِهِم مَّرَضٌ وَٱلْكَٰفِرُونَ مَاذَآ أَرَادَ ٱللَّـهُ بِهَٰذَا مَثَلًا كَذَٰلِكَ يُضِلُّ ٱللَّـهُ مَن يَشَآءُ وَيَهْدِى مَن يَشَآءُ وَمَا يَعْلَمُ جُنُودَ رَبِّكَ إِلَّا هُوَ وَمَا هِىَ إِلَّا ذِكْرَىٰ لِلْبَشَرِ

wa-mā jaʿalnā aṣḥāba l-nāri illā malāʾikatan wa-mā jaʿalnā ʿiddatahum illā fitnatan li-lladhīna kafarū li-yastayqina lladhīna ūtū l-kitāba wa-yazdāda lladhīna āmanū īmānan wa-lā yartāba lladhīna ūtū l-kitāba wa-l-muʾminūna wa-li-yaqūla lladhīna fī qulūbihim maraḍun wa-l-kāfirūna mādhā arāda allāhu bi-hādhā mathalan ka-dhālika yuḍillu allāhu man yashāʾu wa-yahdī man yashāʾu wa-mā yaʿlamu junūda rabbika illā huwa wa-mā hiya illā dhikra lil-bashari

And We have set none but angels as Guardians of the Fire; and We have fixed their number only as a trial for Unbelievers,- in order that the People of the Book may arrive at certainty, and the Believers may increase in Faith,- and that no doubts may be left for the People of the Book and the Believers, and that those in whose hearts is a disease and the Unbelievers may say, "What symbol doth Allah intend by this?" Thus doth Allah leave to stray whom He pleaseth, and guide whom He pleaseth: and none can know the forces of thy Lord, except He and this is no other than a warning to mankind.