Concise Quran Commentary
For each oppressive town that became destroyed, Allah already knew of its fixed time. The destruction will neither come before or after its time.
Tafsir for this Ayah
Surah 15 : Ayah 4
Surah 15 : Ayah 4
وَمَآ أَهْلَكْنَا مِن قَرْيَةٍ إِلَّا وَلَهَا كِتَابٌ مَّعْلُومٌ
We never destroyed any town except that it had a destined time.