[Source]: Han Changli Quanji (The Complete Works of Han Yu) - "Memorial of Thanks upon Appointment as Prefect of Chaozhou": "At this moment, it is truly a joyous gathering, a once-in-a-thousand-years opportunity that cannot be encountered."
[Explanation]: "Zai" means year; "feng" means to encounter. It means an event so rare that it happens only once in a thousand years. It describes an opportunity that is extremely difficult to come by.
Story: Han Yu, the renowned literary figure of the Tang Dynasty, became an orphan at a young age and was raised by his elder brother's wife. He studied diligently on his own. In his youth, he read widely and laid a solid foundation in scholarship. At the age of 35, he went to the capital and served as a Doctor at the Imperial Academy. Later, he was promoted to Vice Minister of Justice. At that time, Buddhism was widespread, and even Emperor Xianzong of Tang greatly revered it. Upon hearing that a temple housed a relic of the Buddha Sakyamuni, the emperor prepared to mobilize a large entourage to welcome it into the palace for worship. Han Yu strongly disapproved and wrote the "Memorial of Advice Against Welcoming the Buddha's Relic" to oppose this. In it, he mentioned that since Buddhism entered China, emperors had not reigned for long; those who sought the Buddha's protection invariably met with tragic ends. After reading this memorial, Emperor Xianzong became extremely angry, believing that Han Yu was not only deliberately opposing him but also using history to imply that his life would be short. Consequently, he intended to execute Han Yu. Fortunately, the prime minister pleaded on his behalf, and the punishment was commuted to demotion, sending Han Yu to serve as Prefect of Chaozhou.
During the mid-Tang Dynasty, central ruling power was gradually weakening. After ascending the throne, Emperor Xianzong reformed some of the previous dynasty's corrupt policies, thus strengthening central authority. Han Yu, demoted to Chaozhou, took note of this situation and again submitted the "Memorial of Thanks upon Appointment as Prefect of Chaozhou" to Emperor Xianzong, lavishly praising the emperor's achievements in order to regain his trust and return to court service. In this memorial, Han Yu flattered Emperor Xianzong as the restorer who had turned the tide and restored prosperity. He further advised the emperor to perform the Fengshan ceremony on Mount Tai. Fengshan is a grand ritual to worship Heaven and Earth. The ancients believed that among the Five Sacred Mountains, Mount Tai was the highest. Building an altar on the summit to worship Heaven is called "Feng," while clearing a site on Liangfu Mountain at the foot of the mountain to worship Earth is called "Shan." Famous historical figures such as Qin Shi Huang and Emperor Wu of Han had both performed this grand ceremony. By making this suggestion, Han Yu was positioning Emperor Xianzong as an emperor of outstanding contribution.
Han Yu also subtly expressed in this memorial his hope that Emperor Xianzong would allow him to participate in the Fengshan ceremony, stating that if he could not attend this once-in-a-thousand-years grand occasion, it would be a lifelong regret. Later, Emperor Xianzong recalled him to the capital and appointed him Vice Minister of the Ministry of Personnel.