During the Five Dynasties period in the Southern Tang kingdom, there was a man named Xu Xuan, renowned for his eloquence, who served successively as Vice Minister of Rites, Hanlin Academician, and Minister of Personnel.
In 960 AD, Emperor Taizu of Song, Zhao Kuangyin, seized power from the Later Zhou dynasty and established the Northern Song. Determined to unify the realm, he systematically conquered the regimes of Jingnan and Later Shu, tightening a strategic noose around the Southern Tang kingdom.
Li Yu, the last ruler of the Southern Tang, was a man of little ability. Knowing his small kingdom could never withstand the mighty Northern Song dynasty, he bowed in submission, sending vast tributes of gold and treasure each year to cling to his throne.
One year, Xu Xuan was sent by Li Yu to escort tribute to the Northern Song court. According to custom, the Song dynasty was to dispatch an official to the border to welcome him and accompany him to the capital. However, the ministers all feared their eloquence was no match for Xu Xuan's and that they would be unable to respond in conversation, so none were willing to go. Emperor Taizu of Song simply selected an illiterate palace attendant to go instead.
As expected, Xu Xuan dominated the welcome banquet with eloquent speeches, every sentence quoting classics and brimming with literary flair, while the Northern Song envoy sat dumbfounded, utterly speechless.
In truth, the Northern Song Dynasty was not lacking in eloquent diplomats, but Emperor Taizu of Song believed that verbal sparring between envoys held little value—the outcome of war between two nations hinged on military strength. So, as soon as Xu Xuan departed, the emperor ordered his great general Cao Bin to intensify troop training, preparing to attack the Southern Tang.
In the autumn of 974 AD, Emperor Taizu of Song used Li Yu's refusal to visit the capital Bianjing as a pretext to launch a massive land and water assault on the Southern Tang kingdom. Seeing his realm on the brink of collapse, Li Yu dispatched the scholar Xu Xuan to Bianjing to plead with the emperor for a temporary halt to the offensive.
Xu Xuan arrived in Bianjing and said to Emperor Taizu of Song, "Li Yu has committed no crime; he serves Your Majesty as a son serves his father. Why does Your Majesty attack him?" Emperor Taizu replied without hesitation, "Li Yu indeed has no fault. But since ancient times, all under heaven is one family. How can I allow another to snore by my bedside?"
Hearing Emperor Taizu's words, Xu Xuan realized the situation was hopeless and had no choice but to turn back.
In the winter of 975 AD, Song forces breached the Southern Tang capital Jinling, ending the kingdom and making its ruler Li Yu a captive.
Later, people used the idiom "How can others be allowed to snore at the bedside?" to describe not allowing others to infringe upon one's own interests.
Source: Yue Ke (Song Dynasty), *History of the Cheng Family*, "Xu Xuan's Diplomatic Mission"
Meaning of the Idiom: Later, the Chinese idiom "卧榻之侧，岂容他人鼾睡" came to describe how not allowing others to infringe upon one's own interests.