Allah is Everlasting (ad-Da’im), i.e., the One whose existence is not followed by non-existence, and it is impossible for annihilation to be attributed to Him. It is a mental impossibility for Allah’s existence to come to an end. Nothing is Everlasting in this way except Allah.
Allah is Everlasting by Himself. Nothing else attributed Allah with Everlastingness. The everlastingness of anything other than Allah, such as Paradise and Hellfire, is by the Will of Allah. Paradise and Hellfire are not everlasting on their own; rather, Allah is the One Who Willed everlastingness for them.