More good Christian dragons! This one is sort of a punishing one, however. It sounds like the Irish kenning of “dragon” for “great warrior” has crept into the story, and they’re talking about a warrior angel.
However, this is from the Vita S. Kannechi, the Life of St. Cainneach of Aghaboe. He was a busy guy — hung out with St. Columba, became famous in Scotland as St. Kenneth or St. Canice, and bopped around the continent a bit before coming home. This was pretty typical for a roaming pilgrim Irish monk back in the day. However, this life was written in the 8th century, so the dragon story is not necessarily anything contemporary to the guy. (The Life of Columba that mentions Cainneach is very contemporary, however.)
Vita S. Kannechi, c. 9:
“Therefore St. Cainneach promised to spend the future, his sepulture, and his resurrection in this offered city with the above-mentioned king. But having frequently visited the saint, the angel of God who had predicted his resurrection in Ireland, rebuked him for the incautious promise. So then St. Cainnech was in anguish, between his promise and the angel’s word.
“But the Lord, the True Judge, helped him. For a fiery dragon descended from Heaven and cut off the outside toe of St. Cainneach’s right foot. St. Cainneach left his toe there, fulfilling his promise; and obeying the angel’s word, he went back to Ireland. Indeed, this above-mentioned king was afterwards a wonderful man and a bishop.”
Only the Irish would link dragons and pinkie toes.