وَاِذْ تَاَذَّنَ رَبُّكَ لَيَبْعَثَنَّ عَلَيْهِمْ اِلٰى يَوْمِ الْقِيٰمَةِ مَنْ يَّسُوْمُهُمْ سُوْۤءَ الْعَذَابِۗ اِنَّ رَبَّكَ لَسَرِيْعُ الْعِقَابِۖ وَاِنَّهٗ لَغَفُوْرٌ رَّحِيْمٌ ( الأعراف: ١٦٧ )
Wa iz ta azzana Rabbuka la yab'asannna 'alaihim ilaa Yawmil Qiyaamati mai yasoomuhum sooo'al 'azaab; inna Rabbaka lasaree'ul 'iqaab; wa innahoo la Ghafoorur Raheem (al-ʾAʿrāf 7:167)
And [mention] when your Lord declared that He would surely [continue to] send upon them until the Day of Resurrection those who would afflict them with the worst torment. Indeed, your Lord is swift in penalty; but indeed, He is Forgiving and Merciful. (Al-A'raf  : 167)
1 Mufti Taqi Usmani
Recall) when your Lord declared that He would surely keep sending, till the Day of Judgment, those who inflict on them evil chastisement. Certainly, your Lord is swift in punishing, and certainly He is the Most-forgiving, Very Merciful.