Mule Without a Bridle
Title figure in a late twelfh-century comic French verse romance by Paien de Maisières.
The bridal that the mule was missing was magic, and whoever held it held the rights to a kingdom. One sister had seized the bridle from another, and the disinherited sister brought the bridle-less mule to Arthur’s court, seeking redress. Kay set out on the quest but failed; Gawain was successful in retrieving the object.
Heinrich von dem Türlin adapted the story in Diu Crône, giving the sisters the names Sgoidamur and Amurfina.
Source
La Mule Sans Frein | Paien de Maisières, late 12th century