When reading in Wikipedia about the Tigris, Euphrates, and other rivers in the general vicinit, I read about a transmitted story of one warrior who, after winnning in battle, washed his sword in the source of a river. Which river and which legend might that have been?
I do not remember enough details, but the episode might be unique enough to be identified. If I remember correctly, the source was located north of Syria, that is in modern Turkey, Georgia, or most likely if memory serves, Armenia.
Whether the story is a myth or based on history I don't know.