What is the Striking Calamity?

And what can make you know what is the Striking Calamity?

It is the Day when people will be like moths, dispersed,

And the mountains will be like wool, fluffed up.

Then as for one whose scales are heavy [with good deeds],

He will be in a pleasant life.

But as for one whose scales are light,

His refuge will be an abyss.

And what can make you know what that is?

It is a Fire, intensely hot.