Tafsir of Ghafir 40:49

And those who are in the Fire—the weak ones and the arrogant ones alike—when schemes became constrained for them and excuses failed them, will say to the Keepers of Hell—that is, to those assigned to torment the inhabitants of the Fire. Although it would be more apparent [grammatically] to refer to its keepers with a pronoun relating to the "Fire," the noun ("Hell") was used in place of the pronoun to instill terror; for Jahannam (Hell) is more specific than al-nar (the Fire), according to the apparent meaning, either because the latter is applied to what exists in this world, or because it is the place of the most severe torment, encompassing the Fire and other things. It is also suggested that this is to specify the location of the disbelievers within the Fire—that Jahannam is the deepest of its pits—derived from their saying "a jahnam well" meaning one that is deep-bottomed. And among them, meaning the disbelievers, are the most rebellious of them. Perhaps the angels appointed to the torment of those ones are more likely to have their supplications answered due to their greater proximity to Allah, the Mighty and Majestic; for this reason, the inhabitants of the Fire single them out with the request for supplication and say to them: "Supplicate to your Lord to lighten for us one day—that is, the measure of one day of the days of this world—from the torment."

That is, [lighten] a portion of the torment; thus, the object of "lighten" is omitted, and "from" serves to explain or denote a part. It is also permissible that the object is "one day," with the genitive construction omitted, as in "the pain of a day," and "from the torment" is its explanation. The intended meaning is: "Avert from us one day of the days of torment."