View source for Tarikh al Dhul-Qarnayn

Tarikh al- Dhul-Qarnayn, chapter 57
  
''in Greek, translated by Leo from the original Arabic''
  
  Dhul-Qarnayn received two prophecies: that he would be killed by a river
  an that after his death his empire would bbe destroyed by the followers
  of Ten-Ghari, who are commonly known to be the tribes of Yajuj and
  Majuj, which teem innumerably in the east.

  Now Dhul-Qarnayn had acquired a ring from deep within the treasure
  houses of Persia, which had once belonged to Kourosh the Great, and this
  ring was such that it would grant three wishes, and these wishes were of
  a most uncommonly powerful nature; but Kourosh never used it, even
  against the forces of Yajuj, which slew him and flayed him and filled
  his skin with blood and made it dance like a puppet.  His son Kambujiya
  used one wish to conquer Misr, which had hitherto not been conquered
  except thrice in the distant past.  Daraya-Wahush used one wish to open
  the tomb of Queen Ni-Tukayrish, which had stymied all human ingenuity to
  open in any other way.  But he then, in frustration, had declared the
  ring a vile bauble, and all but discarded it, so that Dhul-Qarnayn found
  it in his treasure hoard, and kept it with him always, carefully
  planning when to use the wish.  And when he had heard the prophecy of
  the followers of Ten-Ghari, he resolved that although his own flesh may
  perish, his empire must endure, and he wished a mighty wish, and
  conjured up, as the ring crumbled to dust, a giant brazen horn, one of
  the two for which he is famous.  And the horn had this power, that it
  would blow constantly as the wind sailed through, and its volume and
  tone were such that no follower of Ten-Ghari would approach it; and as
  long as it blew, the followers of Ten-Ghari should not respass on the
  empire of Dhul-Qarnayn.  And some say Dhul-Qarnayn had done the world a
  great boon then, for had it not been for this horn, which still winds,
  the people of Yajuj and Majuj, who neither Kourosh nor Dhul-Qarnayn had
  been able to conquer, would have overrun the earth.  But instead they
  are compelled to remain in their homeland, milling eternally.

  And then Dhul-Qarnayn came to the Wadi al Hagarah, also known as the
  river Saba-Tayyah, which runs in a circle and cannot be crossed.  And
  Dhul-Qarnayn was wroth that had used the ring for his brazen horn, for
  feign would he know what was beyond the Wadi al Hagarah.  And six days
  he camped by its shore, waiting for its tumult to die down; but no
  longer.  For on the sixth day, he vowed that he would cross it; and was
  wounded grievously by stones in the attempt; and his men draggd him back
  out, and he said, "A river will be my death, but it will not be this
  one," and he came away from the Wadi al Hagarah and never returned.

  But Dhul-Qarnayn's empire was destroyed at the battle of Ib-zush, when
  the last man who would hold it entire fell before the war elephants. 
  And all elephants, when they are to die, are led by a mysterious being
  named Ten-Ghari to the elephant's graveyard.