According to the English chronicler John of Bromton, sometime in the earlier half of the 12th c the cellar of a monastery in the bishopric of Treves was haunted by an elf.
One morning when the butler entered the cellar, he was mortified to find a whole cask of wine had been emptied during the night, most of the contents spilt out on the floor. The butler chid his servant, locked the door of the cellar and took the key away with him, but the next day, he found that yet another cask of wine had been spoilt and spilt.
The butler went to the father abbot who proceeded to go down to the cellar where he blessed the casks with holy water after which he locked the cellar door and sealed it with the seal of the abbey - taking the key into his own possession. The next morning, he found a small black elf stuck fast to one of the casks.
The abbot took the elf, clothed him in the habit of a monk and kept him in the school of the monastery; where he never grew any bigger.
One day, an abbot from a neighbouring monastery came to examine the scholars, hearing the story, he counselled his brother abbot that he could no longer keep the devil in his house. The moment the monkish habit was removed from the elf, he vanished - never to be seen again.