Quran 74:27-31. And what will make you know (exactly) what Hell-fire is?
It spares not (any sinner), nor does it leave (anything unbunrt). Burning and blackening the skins! Over it are nineteen (angels as guardians and keepers of Hell).
And We have set none but angels as guardians of the Fire. And We have fixed their number (19) only as a trial for the disbelievers, in order that people of the Scriptures (Jews and Christians) May arrive at a certainty (that this Qur’an is truth as it agrees with their Books regarding the number (19) which is written in the Taurat (Torah) and the Injeel (Gospel) and that the believers may increase in Faith (as this Qur’an is the truth), and that no doubt may be left for the people of the Scriptures and the believers, and that those in whose hearts is a disease (of hypocrisy) and the disbelievers may say: “What Allah intends by this (curious) example?” Thus Allah leads astray whom He wills. And none can know the hosts of your Lord but He. And this (Hell) is nothing else than a (warning) reminder to mankind.