During the Spring and Autumn period, Duke Xuan of the state of Chen, wanting to make his favored concubine's son, Prince Kuan, the heir, killed the already-established crown prince, Yü Kou.
Prince Wan, younger brother of Duke Xuan of Chen, was a close friend of Yu Kou. Fearing that the duke might also have him killed, Prince Wan fled Chen and sought refuge in the state of Qi.
At that time, the ruler of Qi was Duke Huan of Qi. Knowing that Prince Wan was a man of both virtue and talent, Duke Huan received him with great respect and intended to appoint him as a high minister. Prince Wan declined, saying, "I am merely a refugee who has sought shelter in your state. I am already deeply grateful that Your Grace has overlooked my crime of fleeing and taken me in—how could I dare to accept such a lofty position? If I agreed, others would mock me."
Duke Huan of Qi heard this, so he no longer appointed him as a grand master but assigned him the role of "Gongzheng," responsible for managing various craftsmen. Although Prince Wan's position was low, Duke Huan's treatment of him was not; he regarded him as a friend, often chatting and playing with him.
One afternoon, Duke Huan of Qi visited Prince Wan's home, where Prince Wan hosted a banquet. As they drank and chatted, night fell unnoticed. Still wanting to continue drinking, Duke Huan ordered lamps lit. Prince Wan politely declined, saying, "I divined for the day, not for the night—I dare not proceed."
This phrase means: "I only prepared to accompany you during the day, not to stay on through the night. Forgive me for not daring to linger longer with you."
With that, Duke Huan of Qi took his leave and returned to the palace.
Later, the idiom "Day and Night Revelry" came to describe continuous, non-stop merrymaking from night until dawn.
Source: *Zuo Zhuan*, Chapter "Duke Zhuang's Twenty-Second Year"
Meaning of the Idiom: Later, the Chinese idiom "卜昼卜夜" came to describe continuous, non-stop merrymaking from night until dawn.