Tafsir of Al-Mu'minoon 23:103

(Meaning the scales of their good deeds, or the deeds that have no weight or consideration, which are their evil deeds. This is what has been said, and it is based on the disagreement regarding the weighing of the deeds of the disbelievers: whoever affirms it says the former, and whoever denies it says the latter. The discussion on the parallel of this verse in Surah al-A'raf has already preceded, so recall it.)

(They have wasted them by squandering the time for their perfection and have nullified their readiness to attain their completion. The demonstrative pronoun in both instances refers to the relative pronoun, and its pluralization is in consideration of its meaning, just as the singularization of the two pronouns in the two relative clauses is in consideration of its wording.)

This is a second predicate for "those." It is also permitted that it be the predicate of an omitted subject—that is, "they are eternal in Hell"—and the sentence is either an initiation brought to explain their loss, or it is also a second predicate for "those." It has also been suggested that "those" acts as an adjective for the demonstrative pronoun, and "eternal" is the predicate.

It is said that "eternal," along with its dependent, is a substitution (badal) for the relative clause. Al-Khafaji said: "That is, a substitution of inclusion (badal al-ishtimal), because their eternity in Hell includes their loss." He made it so, considering that it carries the meaning of "they will abide eternally in Hell," and thus it is suitable to serve as a relative clause, as is required by the rules of substitution from a relative clause. The outward approach of al-Zamakhshari suggests the preference for this view, but to me, it is not a sound view, as its weakness is apparent.

Abu Hayyan critiqued the claim that "in Hell, they are eternal" is a substitution, saying: "This is a strange substitution. Its true nature would require the substitute to be that to which 'in Hell' relates—that is, 'they are settled.' It is as if it is a substitution of one thing for another based on metaphor, because whoever loses his soul is settled in Hell."

You know that the apparent reading is that "in Hell" relates to "eternal," and that relating it to an omitted [predicate] and making that omitted element the substitute—while leaving "eternal" dangling—is not something one should turn to, given the availability of the clear and unforced approach.