فَارْتَقِبْ يَوْمَ تَأْتِي السَّمَاء بِدُخَانٍ مُّبِينٍ
[44:10]
Therefore keep waiting for the day when the heaven shall bring an evident smoke,
Then watch thou for the Day that the sky will bring forth a kind of smoke (or mist) plainly visible,
But watch thou (O Muhammad) for the day when the sky will produce visible smoke