From the personal journals of Starswirl the Bearded:

Now, there was a day when the great chaos spirit Discord decided to challenge a farm mare to see who was the best fiddle player there had ever been, and the challenge was accepted. Now, I've gathered eye witness reports, and I think I've been able to piece together just exactly what went down that faithful day in Ponyville, where a simple mare became a Legend of Magic and showed up the Master of Chaos himself...

(Based on the song "The Devil Went Down to Georgia" by the Charlie Daniels Band. All rights to the song go to them and I make no money off of it.)