Quoted in Prose Edda

Then spoke Third: ‘Just as from Niflheim there arose coldness
and all things grim, so what was facing close to Muspell was hot
and bright, but Ginnungagap was as mild as a windless sky. And
when the rime and the blowing of the warmth met so that it
thawed and dripped, there was a quickening from these flowing
drops due to the power of the source of the heat, and it became
the form of a man, and he was given the name Ymir. But the
frost-giants call him Aurgelmir, and from him are descended
the generations of frost-giants, as it says in the Shorter Voluspa:

All sibyls are from Vidolf, all wizards from Vilmeid, all
sorcerers from Svarthofdi, all giants from Ymir come.


- Prose Edda, Gylfaginning