This is a OLD myth regarding the tempering of “damascus steel” and is utterly without historical or metalurgical basis.
First off, Damascus in Syria was NOT a blade making center–it was a distribution center for a lot of blades–many of them “pattern welded” and then acid etched (strong vinegar) to bring out the unique weld lines.
Second, these so called “damascus blades” were actually from India, and apparently were not even “pattern welded” (which the Celts seemed to be the first to have invented, circa 300 BC) but a form of crude yet effective “crucible steel”, aka “Wootz steel”.
Third, the myth of quenching in the body of a slave seems to be a lay person’s confusion of some smith’s practice of quenching in animal blood–a variation of “brine quench” (salt water solution).
Primary source, Master Bladesmith Jim Hrisoulas of Salamander Armory, author of The Complete Bladesmith and The Master Bladesmith and Forging Damascus Blades, Vols 1 & 2 (Paladin Press