Midrasch zu Ijow 41:5

On the fifth day He brought forth from the water the Leviathan, the flying serpent, and its dwelling is in the lowest waters; and between its fins rests the middle bar of the earth. All the great sea monsters in the sea are the food for the Leviathan. Every day it opens its mouth, and the great sea monster destined to be eaten that day (tries) to escape and flee, but it enters the mouth of the Leviathan; and the Holy One, blessed be He, plays with it, as it is said, "This is the Leviathan, whom thou hast created to play with him" (Ps. 104:26).