لَّـٰبِثِينَ فِيهَآ أَحْقَابًا
Sentence structure
لَّـٰبِثِينَ describes the transgressors' state as they remain in Hell. فِيهَآ is linked to this participle, and أَحْقَابًا specifies the duration: ages upon ages.
لَّـٰبِثِينَ — remaining
Grammar: An accusative sound masculine plural active participle functioning as حال of the transgressors. Its singular is لَابِث.
فِيهَآ — therein
Grammar: فِى is a preposition, and هَا is a third-person feminine singular pronoun in the genitive position referring to Hell. The phrase is linked to لَّـٰبِثِينَ.
أَحْقَابًۭا — for ages
Grammar: An indefinite accusative broken plural functioning as an adverb of time. Its singular is حُقُب.