Cantiga 19 of the Cantigas de Santa Maria of Alfonso X

The Three Knights
Three men chased an enemy of theirs into a church and locked him in.
They then hacked him to death in front of the altar.
They tried to leave the church, but could not.
They could not grasp their weapons and their bodies became inflamed.
They begged the Virgin for mercy, repented of their sins, and were cured.
They confessed to the archbishop who told them to go into exile. The swords with which they had killed the man were made into girdles, which they wore as penance as they wandered through Sicily.
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