Tafsir of Al-Ma'aarij 70:8

"The Day the heaven shall be as molten copper (al-muhl)" — it is said that this is connected to 'near' (in the previous verse), or to an implied word indicated by the context, which is 'taking place' (waqi'un) or 'it will occur' (yaqa'u). It may also be a substitute (badal) for "in a Day" (fi yawmin), if the cause of the delay is linked to it, rather than to "ascending" (ta'arruju). The accusative case (nasb) is in consideration of the fact that the position of the prepositional phrase is as such; it is not a substitute for the genitive alone. Therefore, Abu Hayyan’s condition for observing the position—that the preposition be redundant or similar to it, like rubba—is incorrect. Nor does validating the substitution require committing to the view that the vowel of "Day" (yawma) is fixed (mabni), based on the school of the Kufans who permit such a thing even if it is annexed to an indeclinable word.

He mentioned that according to these three estimations, the intended meaning of "the punishment" is the punishment of the Resurrection. As for if the punishment of the world is intended, then it is necessary that the estimation be: "The Day the heaven shall be... such and such will happen." It is as if, because they hastened the punishment, they were answered with the imminence of its occurrence. Then it was said: "Let that be trivial compared to what is prepared for you on the Day the heaven shall be as molten copper." In that case, the punishment is the punishment [itself].

It is not hidden that substitution is possible, even if one considers "on a Day" to be connected to "ascending," based on the fact that the intended meaning of that is also the Day of Resurrection, as we have previously stated. It is preferable, when it connects to "near," that "near" not be intended in the sense of essential possibility, because qualifying it with "the Day" creates a kind of ambiguity. And if the two pronouns in "they see it" and "We see it" refer to the Day of Resurrection, it necessitates the occurrence of time within time in our statement "It occurs on the Day of Resurrection on the Day the heaven shall be as molten copper," to which a response is provided that is well-known.

In al-Bahr, it is permitted that it be a substitute for the pronoun in "We see it" if it returns to the Day of Resurrection. In al-Irshad, it is suggested it is connected to "there is no preventer for it." Some say it is a direct object to an omitted verb, and its connection to "We see it," as Makki stated—"We do not see it"—is similar to its connection to "they are made to see each other," as he narrated. Similar to this is what might be said regarding its connection to "wishes" (yawaddu) which comes later, so reflect upon this.

"Al-Muhl": Ahmad, al-Diya’ in al-Mukhtara, and others narrated from Ibn Abbas that it is the dregs of oil—that which remains at the bottom of it. Many others said: al-Muhl is that which has been melted slowly (ma'dhub 'ala muhl) from ores. The intended meaning is: "The Day the heaven shall be fragile." Abd ibn Humayd narrated from Qatada regarding the verse that the heaven is green now, and that on the Day of Resurrection, it will change to another color, turning to redness.