1st Book of Enoch Chapt. 17:1-8

Enoch's Journeys through the Earth and Sheol.
5. And I came to a river of fire in which the fire flows like water and discharges itself into the great sea towards the west. 6. I saw the great rivers and came to the great ⌈river and to the great⌉ darkness, and went to the place where no flesh walks.