﴿ فَكَذَّبُوهُ فَأَخَذَهُمْ عَذَابُ يَوْمِ ٱلظُّلَّةِ ۚ إِنَّهُۥ كَانَ عَذَابَ يَوْمٍ عَظِيمٍ ﴾

“But they gave him the lie. And thereupon suffering overtook them on a day dark with shadows: and, verily, it was the suffering of an awesome day!”

(But they denied him) they denied his message, (so there came on them the retribution of the day of gloom) the punishment came in the form of a cloud that stopped above them and burned them with its heat. (Lo! it was the retribution of an awful day) it was a severe day of chastisement for them.