Caution: Translations of Quran and Ḥadīth may lead to possible misapplications and misinterpretations. This site is intended for students of sacred knowledge that are proficient in comprehending classical Arabic and have a strong foundation in Islamic sciences. Also note that religious injunctions rely on several aspects beyond what one may glean through reading individual aḥādīth.
Qurʾān Bukhārī Muslim Nasāʾī Abū Dāwūd Tirmidhī Ibn Mājah Mālik Aḥmad Dārimī Ḥākim Ibn Ḥibbān Ṭabarānī Nasāʾī's Kubrá Bayhaqī al-Luʾluʾ wa-al-Marjān Ibn Rajab's Fifty Riyāḍ al-Ṣāliḥīn Aḥmad's Zuhd Suyūṭī
quran:18:87 –

He said, "As for one who wrongs, we will punish him. Then he will be returned to his Lord, and He will punish him with a terrible punishment.  

He said, ‘As for him who does wrong, by way of ˹practising˺ idolatry, we shall chastise him, We shall slay him. Then he shall be returned to his Lord and He shall chastise him with an awful chastisement (read nukran or nukuran), that is, a severe ˹one˺, in the Fire.
القرآن:١٨:٨٧ –

قَالَ أَمَّا مَنْ ظَلَمَ فَسَوْفَ نُعَذِّبُهُ ثُمَّ يُرَدُّ إِلَىٰ رَبِّهِ فَيُعَذِّبُهُ عَذَابًا نُكْرًا  

{قال أما من ظلم} بالشرك {فسوف نعذبه} نقتله {ثم يُرد إلى ربه فيعذبه عذابا نكرا} بسكون الكاف وضمها شديدا في النار.