﴿ خَٰلِدِينَ فِيهَا مَا دَامَتِ ٱلسَّمَٰوَٰتُ وَٱلْأَرْضُ إِلَّا مَا شَآءَ رَبُّكَ ۚ إِنَّ رَبَّكَ فَعَّالٌۭ لِّمَا يُرِيدُ ﴾

“therein to abide as long as the heavens and the earth endure-unless thy Sustainer wills it otherwise: for, verily, thy Sustainer is a sovereign doer of whatever He wills.”

abiding therein for as long as the heavens and the earth endure that is for the length of the duration of both in this world except other than what your Lord may will in the way of adding to the duration of these two such that it their abiding becomes indefinite meaning that they will abide therein forever. Truly your Lord is Doer of what He desires.