Where did Cao Cao beat the coke with water?

The story of Cao Cao's dumplings is not in Romance of the Three Kingdoms, but in unofficial history's Biography of Young Children by Liu Zhao, a A Liang native in the Northern and Southern Dynasties. The story says that when Cao Cao was ten years old, he once swam in Longtan and suddenly met a fierce crocodile (the story of a young child said it was jiaozi, but it was actually a crocodile). Crocodiles bared their teeth and attacked Cao Cao, but Cao Cao was fearless and calmly responded to crocodiles. The crocodile couldn't eat anything and ran away. After Cao Cao came home, he didn't mention the crocodile to his family. Later, an adult flinched when he saw the snake. Cao Cao laughed and said innocently, "I am not afraid of crocodiles in Longtan, but you are afraid of a snake." That's ridiculous! " When people asked, Cao Cao told them the truth, and they all marveled at the courage of the young Cao Cao.