Loke Laufey’s son had once craftily cut all the hair off Sif; but when Thor found it out he seized Loke, and would have broken every bone in him, had he not pledged himself with an oath to get the swarthy elves to make for Sif a hair of gold that should grow like other hair.

- Prose Edda (Loke's Wager With The Dwarfs)