It's from Du Fu's "Nine Fortunes, Six Fortunes" in the Tang Dynasty. The whole poem is:
Bow should be used as a strength, and arrow should be used as a length. The Shoot shall shoot the horses, and the leaders shall capture their leaders.
Killing people is limited, and countries have their own borders. As long as you can stop the enemy's invasion, is it possible to fight is to kill more people?
Translation:
Bow should be the hardest, and archery should be the longest. If you shoot a man, you must shoot a horse. If you catch a thief, you must catch their leader.
There should be restrictions on killing people, and all countries have borders. As long as we can stop the enemy's aggression, is it necessary to fight to kill more people?
Extended information
Creation background:
This poem was written in the eleventh year of Bao (752) and is a series of poems with military themes. This period was also the growing period of the Tang Dynasty, which was accompanied by the military expansion of the Tang Dynasty. Most of the predictions of the imperial court were optimistic, but Du Fu did not quite agree with the military line of Xuanzong of the Tang Dynasty.
About the author:
Du Fu (712 -77), with beautiful words, was a great realistic poet in Tang Dynasty, and was called "Li Du" together with Li Bai. Originally from Xiangyang, Hubei Province, he moved to Gongxian County, Henan Province. In order to distinguish Li Shangyin and Du Mu from "Little Li Du", Du Fu and Li Bai are also called "Great Li Du", and Du Fu is often called "Old Du".
As a teenager, Du Fu traveled to wuyue and Qi Zhao successively, during which he went to Luoyang. After the age of thirty-five, I took the exam in Chang 'an first, and came last. Later, he presented a gift to the emperor and presented it to the nobles. The officialdom was frustrated and witnessed the extravagance and social crisis of the upper class in the Tang Dynasty. In the fourteenth year of Tianbao (755), the Anshi Rebellion broke out, Tongguan fell, and Du Fu moved to many places.
In the second year of Ganyuan (759), Du Fu abandoned his official position and went to Sichuan. Although he escaped from the war and lived a relatively stable life, he still cared about the whole life and the state. He created famous works such as Ascending the Mountain, Spring Hope, Northern Expedition, Three Officials and Three Farewells. Although Du Fu is a realistic poet, he also has a wild and uninhibited side. It is not difficult to see Du Fu's heroism and dry clouds from his masterpiece "Song of the Eight Immortals in Drinking".
In the winter of the fifth year of Dali (77), Du Fu died of illness at the age of 59. Du Fu's influence on China's classical poetry is far-reaching, and he is called "the sage of poetry" by later generations, and his poems are called "the history of poetry". Later generations called him Du Shiyi and Du Gongbu, and also called him Du Shaoling and Du Caotang.
Baidu Encyclopedia-Nine Frontiers, Part Six