Tafsir of Al-Isra 17:8

{It may be that your Lord will have mercy upon you} after the second time, if you repent a second repentance and refrain from acts of disobedience.

{But if you return [to sin], We will return [to punishment]} a third time. They did return, so Allah returned the retribution upon them by empowering the Persians against them and imposing tribute upon them.

• Al-Hasan said: They returned, so Allah sent Muhammad (ﷺ), and they now pay the Jizya (tribute) while they are humbled.
• Qatada said: The final outcome of that was that Allah sent this tribe of the Arabs against them, and they remain in torment from them until the Day of Resurrection.

{A prison} meaning a place of confinement. It is said of a prison that it is muḥṣar or ḥaṣīr.

• Al-Hasan said: A mat (bisāṭ), just as a woven mat is spread out.

{Indeed, this Qur’an guides to that which is most upright and gives good tidings to the believers who do righteous deeds that they will have a great reward. And that those who do not believe in the Hereafter—We have prepared for them a painful punishment.}