Vita Sancti Euflami (Life of Saint Efflam(m)). c AD 1100:

Spence, Lewis. Legends & Romances of Brittany, pp278-281, 340-342, 366. New York: Frederick A Stokes Company Publishers, 1917.
   https://www.gutenberg.org/files/30871/30871-0.txt
   https://ia800306.us.archive.org/30/items/legendsromanceso00spen_0/legendsromanceso00spen_0.pdf