Luqman 31:9

Khalideena feeha waAAda Allahihaqqan wahuwa alAAazeezu alhakeem

Wherein they abide eternally; [it is] the promise of Allāh [which is] truth. And He is the Exalted in Might, the Wise.

in which they will live forever - an absolute promise of Allah. He is the Mighty, the Wise.