Snorri Sturluson – The Younger Eddas (ca 13th century)

“After this, the gods despaired of ever being able to bind the wolf; wherefore All-father sent Skirnir, the messenger of Frey, into the country of the Dark Elves (Svartalfaheim) to engage certain dwarfs to make the fetter called Gleipnir. It was fashioned out of six things; to wit, the noise made by the footfall of a cat; the beards of women; the roots of stones; the sinews of bears; the breath of fish; and the spittle of birds. Though thou mayest not have heard of these things before, thou mayest easily convince thyself that we have not been telling thee lies. Thou may have seen that women have no beards, that cats make no noise when they run, and there are no roots under stones. Now I know what has been told thee to be equally true, although there may be some things thou art not able to furnish a proof of.”

“Binding the Wolf Fenrir”