Surah Ad-Dukhan, ayah 10

فَٱرۡتَقِبۡ يَوۡمَ تَأۡتِي ٱلسَّمَآءُ بِدُخَانٖ مُّبِينٖ ١٠

Fartaqib yawma ta'tis-samā'u bidukhānim mubīn

Then watch for the Day when the sky will bring a visible smoke