Once upon a time, a man named Hu-Wu-Bau, who lived near the Great Mountain, went for a walk there one day. Under a tree, he met a messenger in a red robe who called out to him, "The Lord of the Great Mountain would like to see you!" The man was very frightened but didn't dare object. The messenger told him to close his eyes, and when he opened them again after a short time, he found himself standing before a grand palace. He entered to see the god. The god had a meal prepared for him and said, "I only sent for you today because I heard you planned to travel to the West. In that case, I'd like to give you a letter to take to my daughter."

"But where is your daughter?" asked the man.

"She is married to the river-god," was the reply. "All you need to do is take the letter there. When you reach the middle of the Yellow River, knock on the side of the ship and call out, 'Greencoat!' Then someone will appear and take the letter from you."

With these words, he handed Hu-Wu-Bau the letter, and he was taken back to the upper world.