Surah Al-Kahf — Ayah 58 (18:58)
وَرَبُّكَ ٱلۡغَفُورُ ذُو ٱلرَّحۡمَةِۖ لَوۡ يُؤَاخِذُهُم بِمَا كَسَبُواْ لَعَجَّلَ لَهُمُ ٱلۡعَذَابَۚ بَل لَّهُم مَّوۡعِدٞ لَّن يَجِدُواْ مِن دُونِهِۦ مَوۡئِلٗا ٥٨
English translation (Saheeh International)
And your Lord is the Forgiving, the possessor of mercy. If He were to impose blame upon them for what they earned, He would have hastened for them the punishment. Rather, for them is an appointment from which they will never find an escape.
Brief commentary
In order for the Prophet (peace be upon him) not to look forward to a hasty punishment for those who rejected him, Allah said to him: Your Lord - O Messenger - is One Who forgives the sins of those who repent, and One Whose Mercy encompasses everything. It is out of His mercy that he grants respite to sinners in order for them to repent to Him. If He was to punish these people who turn away, He would have hastened the punishment for them in the worldly life. But He is tolerant and merciful. He delayed the punishment so that they repent. They have an appointed time and place in which they will be recompensed for their disbelief and turning away if they do not repent, from which they will find no escape.