وَلَوْلَا كَلِمَةٌ سَبَقَتْ مِنْ رَّبِّكَ لَكَانَ لِزَامًا وَّاَجَلٌ مُّسَمًّى ۗ ( طه: ١٢٩ )
Wa law laa Kalimatun sabaqat mir Rabbika lakaana lizaamanw wa ajalum musammaa (Ṭāʾ Hāʾ 20:129)
And if not for a word that preceded from your Lord, it [i.e., punishment] would have been an obligation [due immediately], and [if not for] a specified term [decreed]. (Taha  : 129)
1 Mufti Taqi Usmani
But for a word from your Lord that had passed earlier, and an appointed time that had been fixed, it (the punishment) would have been inevitable (for them).