Haritamaṇḍūka Jātaka (No.239)
The Bodhisatta was once born as a green frog. A water snake, looking for fish, fell into a wicker cage set by men to catch fish. The fish, seeing the snake, bit him until he fled, dripping with blood. Exhausted, he lay on the edge of the water. Seeing the green frog at the mouth of the cage, the snake asked him if the fish had done right in attacking him. “Why not?” asked the frog; “you eat fish which get into your place and they eat you when you get into theirs.” The fish, hearing this, fell upon the snake and did him to death.
The story was related in reference to Ajātasattu’s war with Pasenadi. When he was victorious, Ajātasattu showed great delight, but when he lost he was quite downcast. The snake is identified with Ajātasattu. J.ii.237‑39.