Even before Cao Pi became the first emperor of Wei, he harbored deep resentment toward his imperial advisor, Bao Xun. The only reason he held back was that Bao Xun was the son of Bao Xin, the man who had once saved Cao Cao's life.
Bao Xun was a man of unwavering integrity who never compromised his principles for personal favor, and he frequently admonished Cao Pi. This constant counsel made Cao Pi feel perpetually constrained, breeding a deep-seated resentment in his heart.
Cao Pi’s former wife had a brother who, abusing his official position, embezzled public funds and was sentenced to death by law. Cao Pi pleaded for him with Cao Cao, but the official Bao Xun opposed it. Furious yet powerless, Cao Pi harbored a grudge against Bao Xun.
After Cao Cao's death, Cao Pi became Emperor Wen of Wei. Seeing the emperor indulging in pleasure, Bao Xun reminded him, "As a new ruler, your priority should be strengthening the military and developing agriculture. Matters like building pavilions and gardens can wait until finances allow." The emperor was greatly displeased by this.
After some time, Emperor Wen wanted to go hunting, but Bao Xun again advised him: "The ancient Three Kings and Five Emperors all governed the world with filial piety. You should do the same—how can you go hunting during the mourning period?"
This time, Emperor Wen ignored his advisor's protests, insisting on taking a few attendants out for a thrilling hunt, and enjoyed himself to the fullest.
Later, Emperor Wen led his troops back from a campaign and halted at Chenliu Commandery to rest. Chenliu's governor, Sun Yong, an old friend of Bao Xun, heard that Bao Xun was with the army and came to visit him. According to regulations, visitors had to enter through the main gate of the camp. But since the army had just stopped and the camp wasn't fully built—only low walls marked the boundaries—Sun Yong stepped over the markers to take a shortcut and catch up with his friend. The camp supervisor, Liu Yao, tried to stop him, but Bao Xun, seeing the camp was incomplete, urged Liu Yao, 'Let it slide this time—let him in.'
After the army returned to Luoyang, Liu Yao made a mistake, and Bao Xun proposed that he be dismissed and sent home. Liu Yao, resentful, secretly reported to Emperor Wen that Bao Xun had allowed Sun Yong to enter the military camp without authorization. Bao Xun had never made a mistake before, but now Emperor Wen seized on this pretext, making a mountain out of a molehill, and ordered Bao Xun to be handed over to the Tingwei for punishment. The Tingwei decided on "a sentence of five years in prison." However, the Three Officials overruled this, stating, "According to law, a fine of two jin of gold is sufficient." Upon hearing this, Emperor Wen flew into a rage and said, "This Bao Xun does not deserve to live, and you dare to let him off! Arrest those Three Officials and lock them up with that group of wicked and treacherous criminals, like 'ten rats in one hole'!"
Emperor Wen's decision was clearly to vent personal spite. The Grand Commandant and Minister of Education all pleaded for Bao Xun, citing that "Bao Xun's father rendered meritorious service to Grand Ancestor (Cao Cao)" as a reason to request clemency. Emperor Wen refused, insisted on executing Bao Xun, and removed the thorn in his side.
Later, the idiom "Ten Rats in One Hole" came to be used to describe villains gathering and fighting among themselves.
Source: *Records of the Three Kingdoms*, "Book of Wei: Biography of Bao Xun"
Meaning of the Idiom: Later, the Chinese idiom "十鼠同穴" came to describe villains gathering and fighting among themselves.