"And what will make you know exactly what Hell-fire is? It spares not (any sinner), nor does it leave (anything unburnt)! Burning 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 only as a trial for the disbelievers - in order that the People of the Scripture may arrive at a certainty and the believers may increase in faith . . ." [74:27-31]