The fog locks the top of the mountain, and the water reaches the sky and the tail. Which ancient poem is it from?

“The fog locks the top of the mountain, and the sky connects the water and the tail water connects the sky” comes from a couplet on Gulangyu Island in Xiamen, Fujian. This is a pair of palindrome couplets that are both literal and logical when read both directly and backwards. They are also known as "reverse couplets" and "roller curtain pairs". They are unique in conception and clever in combination, making them interesting to read.

The meaning of the couplet is that the fog is thick and the mountains in the distance cannot be seen clearly; the water and sky are the same color, and the sky and water are connected. Gulangyu Island in Xiamen is located in the sea. The island is surrounded by mountains and peaks, shrouded in smoke, and the sea is vast and the water is far away from the sky.

Extended information:

At the end of the Ming Dynasty, Liu Rushi, a famous prostitute in the south of the Yangtze River, supported the struggle against the Qing Dynasty and the restoration of the Ming Dynasty. After the death of Ming Dynasty, she hanged herself for this reason. Someone wrote a palindrome couplet praising her:

A willow among people is like this,

She is like a person among willows.

In view of Liu Rushi's noble integrity, Lian Yun said, "Liu Rushi is among the best".

In the Qing Dynasty, there was a famous restaurant in Beijing called "Tianranju". Emperor Qianlong once enjoyed a delicious meal in this building. When he was drunk, he felt as if he was a guest in heaven. So, with a stroke of his pen, he wrote this palindrome couplet:

The guest lives in nature,

He is actually a guest in heaven.

This couplet has one meaning when read sequentially, and another meaning when read backwards. Moreover, the two meanings are interrelated and natural.