Tafsir of An-Naba' 78:17-20

{It was a fixed time} It was, in the decree and judgment of Allah, a limit by which the world is timed and at which it ends; or a limit for the creatures to which they arrive.

{The Day the Trumpet is blown} This is a substitute (badal) for "the Day of Decision," or an explanatory apposition (‘atf bayan).

{And you will come forth in multitudes} From the graves to the place of standing, as nations—each nation with its leader. It is also said: as various groups.

Regarding this, Mu’adh (may Allah be pleased with him) asked the Messenger of Allah (peace be upon him), who replied: "O Mu’adh, you have asked about a momentous matter." Then his eyes welled up and he said: "My nation will be gathered in ten categories:

1. Some in the form of monkeys (the slanderers).
2. Some in the form of swine (those who consume illicit wealth).
3. Some inverted: their feet above their faces, dragged upon them (the usurers).
4. Some blind (those who act unjustly in judgment).
5. Some deaf and dumb (those who are conceited regarding their deeds).
6. Some chewing their tongues, which hang down onto their chests, with pus flowing from their mouths, causing the people of the gathering to loathe them (the scholars and storytellers whose words contradicted their deeds).
7. Some with hands and feet severed (those who harm their neighbors).
8. Some crucified on trunks of fire (those who incite authorities against people).
9. Some more foul-smelling than corpses (those who pursue lusts and pleasures while withholding Allah’s right from their wealth).
10. Some clothed in long garments of tar stuck to their skins (the people of arrogance, pride, and vanity)."

{And the heaven is opened} Read as futtihat (with tashdid) and futihat (with takhfif). The meaning is the abundance of its gates opened for the descent of the angels, as if it were nothing but opened gates—similar to His saying: “And We caused the earth to gush with springs” (Al-Qamar: 12), as if the whole earth were gushing springs.

It is also said: The "gates" are paths and ways; meaning, it is scraped away, its place opens up, and it becomes paths.

{And it becomes a mirage} As in His saying: “And become dust dispersed” (Al-Waqi’ah: 6). It means it becomes something that is nothing, due to the scattering of its parts and the dispersion of its substances.

{Indeed, Hell has been a place of ambush, for the transgressors a place of return, remaining therein for ages. They will not taste therein any coolness nor drink, except scalding water and pus—an appropriate recompense. Indeed, they were not expecting an account, and they denied Our verses with [emphatic] denial. But all things We have enumerated in writing. "So taste [the penalty], and never will We increase you except in torment."}