Surah 77. Al-Mursalat, Ayah 30

I.e., of death, resurrection and God's judgment, all three of which cast dark shadows, as it were, over the sinners' hearts.

The Sinners, instead of reposing in cool shades, will only see the blazing Fire. The only shadow they will see will be that of Smoke, ascending in three columns, right, left, and above, i.e., completely enveloping them. But it will give no comfort or coolness. On the contrary, it will contain huge sparks.