Wathkur akha AAadin ith anthara qawmahu bil-ahqafi waqad khalati annuthuru min bayni (surah Ahqaf: 21)

Tafseer Tafheem-ul-Quran by Syed Abu-al-A'la Maududi

(46:21) Recount to them the story of (Hud), the brother of (the tribe of) 'Ad. Hud warned his people beside the sand-dunes *25 ' and there have been other warners before him and since his time ' saying: 'Serve none but Allah. Verily I fear that the chastisement of an awesome day shall come upon you.'

Wazkur akhaa `Aad, iz anzara qawmahoo bil Ahqaafi wa qad khalatin nuzuru mim baini yadaihi wa min khalfiheee allaa ta`budooo illal laaha inneee akhaafu `alaikum `azaaba Yawmin `azeem

*25) As the chiefs of the Quraish had a false pride of their superiority and exulted in their wealth and prosperity, the story of `Ad is being related to them about whom it was well known that they had been the mightiest people in Arabia.
Literally, Ahqaf (pl. of hiqf) are long dunes of sand less in height than mountains, but technically it is a name given to the southern-western part of the Arabian desert (Ar-Rub'ul-khali) which is wholly un-inhabited. Please see the map on page 672.
Ibn Ishaq says that the territory of 'Ad extended from 'Oman to Yaman, and the Qur'an tells us that they actually belonged to Al-Ahqaf from where they spread to the adjoining lands and subdued weak nations. 125 miles to the north of the present-day city of Makkah there is a place in Hadramaut, where the people have built a tomb to the Prophet Hud, and the place is well known as the Grave of Hud. A religious festival is held there on the 15th of Sha'ban and thousands of people from different parts of Arabia gather there annually. Although it is not historically established, the grave's being built there and the southern Arabs' visiting it in large numbers is at least a proof that local tradition regards this very territory as the land of `Ad. Besides, there are several nuns in Hadramaut which the natives still call by the name of Dar-'Ad (Abode of 'Ad).
From the present condition of Al-Ahqaf no one can even imagine that this land might have been the home of a mighty people boasting of magnificent civilization. Probably it was a green and fertile land thousands of years ago, and then the change of climate might have turned it into a sandy desert. Today it is a vast, wind-swept desert, and no one can dare go into its interior. In 1843 A.D. a Bavarian soldier was able to reach its southern edge. He says that if one looks down from the northern plateau of Hadramaut one can see this desert about a thousand feet in the depression. Here and there in it there are white areas where if a thing falls it goes on sinking into the sand and decays. The Arab Beduins fear this land and arc never willing to step into it at any cost. Once when the Bedouins were not ready to take him there, he went by himself. He says that the sand there is very fine powder, and when he threw a plummet into it from a distance, it sank into it within five minutes and the end of the line to which it was attached, also decayed.
For detailed information, sec:
Arabia and The Isles, Harold Ingrams, London, 1946.
The Unveiling of Arabia, R H. Kirnan, London, 1937.
The Empty Quarter. Philby. London, 1933.