Al A‘rāf

وَكَم مِّن قَرْيَةٍ أَهْلَكْنَاهَا فَجَاءهَا بَأْسُنَا بَيَاتًا أَوْ هُمْ قَآئِلُونَ

فَمَا كَانَ دَعْوَاهُمْ إِذْ جَاءهُمْ بَأْسُنَا إِلاَّ أَن قَالُواْ إِنَّا كُنَّا ظَالِمِينَ

4. "And how many a town that We have destroyed, Our punishment came unto them by night or while they slept at midday."
5. "So their cry, when Our punishment came unto them, was not save that they said: 'Verily we were unjust '."

In the previous verse, people were commanded to follow the Qur'an, and to leave out following anything other than the Qur'an. Now, this verse reminds them the fate of the past unjust nations so that they may fear and not to repeat the manner of those nations. It says:

Allah says that He has destroyed many people of the towns, and the Divine punishment was sent down over them by night or when they were relaxing at noon. It is obvious that having chastisement in such times is more dangerous for people than in some other times.

When Allah’s chastisement was sent down, the only matter they stated was that they said that they were unjust. Thus, when they saw the punishment of Allah with their own eyes, or when they were involved in the Divine chastisement and were still rather alive, they began to confess their faults. This indicates that admission, confession of one's sins, and repentance at the time of befalling calamities and wretchedness are not beneficial for the one.