Explained in detail - Fussilat

Say: What! do you indeed disbelieve in Him Who created the earth in two periods, and do you set up equals with Him? That is the Lord of the Worlds.

And He made in it mountains above its surface, and He blessed therein and made therein its foods, in four periods: alike for the seekers.

Then He directed Himself to the heaven and it is a vapor, so He said to it and to the earth: Come both, willingly or unwillingly. They both said: We come willingly.

So He ordained them seven heavens in two periods, and revealed in every heaven its affair; and We adorned the lower heaven with brilliant stars and (made it) to guard; that is the decree of the Mighty, the Knowing.

But if they turn aside, then say: I have warned you of a scourge like the scourge of Ad and Samood.

When their apostles came to them from before them and from behind them, saying, Serve nothing but Allah, they said: If our Lord had pleased He would certainly have sent down angels, so we are surely unbelievers in that with which you are sent.

Then as to Ad, they were unjustly proud in the land, and they said: Who is mightier in strength than we? Did they not see that Allah Who created them was mightier than they in strength, and they denied Our communications?

So We sent on them a furious wind in unlucky days, that We may make them taste the chastisement of abasement in this world's life; and certainly the chastisement of the hereafter is much more abasing, and they shall not be helped.