为虎作伥 — “To act as an accomplice to a villain”

During the Changqing reign of Emperor Muzong of Tang, there was a recluse named Ma Zheng. He heard that a Fuhu (Tiger-Subduing) Abbot lived on Zhurong Peak of Mount Heng. Taking a young servant with him, he ascended the mountain to visit the abbot.

Upon reaching Zhurong Peak, he found a Buddhist temple where an old monk with white hair and beard resided. The old monk warmly insisted that Ma Zheng stay for a meal, but they had just run out of cooking oil and salt. Ma Zheng sent his servant down the mountain to buy some.

The old monk accompanied them out of the temple gate. Ma Zheng then stood alone by the temple, admiring the mountain scenery. At this moment, another hermit named Ma Zhao approached from down the mountain. After they introduced themselves, Ma Zhao mentioned that halfway up the mountain, he had seen a fierce tiger calling out a person. Ma Zheng inquired about the person's age, appearance, and clothing, and then exclaimed in surprise, "That's my servant!"

Ma Zhao added, "What's strange is that after the tiger ate the person, it suddenly transformed into an old monk with white hair and beard." Soon after, the old monk returned, and Ma Zhao quietly whispered to Ma Zheng, "It's this very monk."

As night fell, the old monk offered them accommodation in the monks' quarters, but they preferred to stay in the dining hall. They securely bolted the door and observed the movements outside. In the middle of the night, a tiger repeatedly tried to ram the door, but they held it firmly, preventing it from breaking open.

Determined to eliminate the man-eating tiger, they finally devised a clever plan. The next morning, they claimed that strange noises were coming from a well in the backyard and lured the old monk to its edge. When the old monk leaned in to look, Ma Zhao forcefully pushed him into the well. As soon as the monk fell into the water, he immediately transformed into a tiger. They then moved large stones and crushed it to death.

When descending the mountain, they lost their way. Fortunately, they later encountered a hunter and spent the night in a shelter built in a tree. In the middle of the night, Ma Zheng was suddenly awakened by human voices below the tree. By the moonlight, he saw dozens of people shouting that they wanted to avenge the tiger. The hunter informed them that these were all people who had been eaten by the tiger, and after death, they had become *chang* ghosts, specifically leading the way for the tiger. Ma Zheng cursed, "You *chang* ghosts, you were devoured by the tiger, yet you still weep and seek revenge for it!"

According to ancient legends, people eaten by tigers would transform into *chang* ghosts after death, continuing to serve the tiger. The idiom "为虎作伥" (wèi hǔ zuò chāng), meaning 'to act as an accomplice to a villain,' originates from this story.