The Prophet's ponies

I was intrigued by a sentence in Michael Chabon's Gentleman of the Road which says something about Hillel, whose mother's blood runs all the way back to one of the five mares of the Prophet. I was curious if Arabian horses really do go back to mares owned by the Prophet so today I asked a Muslim friend of mine, who unfortunately isn't really up on horse knowledge, so next I tried Uncle Google.

I found a couple of conflicting stories. The most popular seems to be that the Prophet's herd of horses hadn't had any water in two days (!) and finally scented some and were running towards it when he called them and only five came to him instead of going on to drink. Those five became the foundation mares for the dynasty.

This site, http://www.athelstan-arabians.com/ArabiansHistory/Arabian1.htm, has a couple of other stories, which are rather old and quite interesting.

Because all Thoroughbreds, or race horses, are descended from one of three founding sires; the Darley Arabian, the Godolphin Arabian and the Byerly Turk, does that mean that most Thoroughbreds are descended from the Prophet's mares? Doesn't that just spark your imagination? What stories you could tell based on just that one speculation.