Tafsir of Sad 38:56

Hell: Its grammatical analysis is known from what has preceded. His saying, Glory be to Him, "they shall enter it" (yaṣlawnahā): meaning they shall enter it and suffer its heat. It is a state (ḥāl) from Hell itself, or from the hidden pronoun in the predicate of inna which refers back to "the evil return" (sharr ma'āb), implying it is Hell. The state is prospective (muqaddarah).

"And wretched is the resting place": That is, it—meaning Hell—is wretched. Thus, the specific subject of condemnation (al-makhṣūṣ bi-al-dhamm) is omitted. Al-mihād (the resting place) is like al-firāsh (the bed/mattress) in both wording and meaning. It is metaphorically derived from that which a sleeper spreads out [to lie upon]. Al-mahd (the cradle) is like al-mihād, and it is sometimes specifically used for the place where an infant is laid.