Tao Te Ching · Ch. 31

夫兵者,不祥之器,物或惡之,故有道者不處。君子居則貴左,用兵則貴右。兵者不祥之器,非君子之器,不得已而用之,恬淡為上。勝而不美,而美之者,是樂殺人。夫樂殺人者,則不可得志於天下矣。吉事尚左,凶事尚右。偏將軍居左,上將軍居右,言以喪禮處之。殺人之衆,以悲哀泣之;戰勝以喪禮處之。

Fú bīng zhě, bù xiáng zhī qì, wù huò wù zhī, gù yǒu dào zhě bù chǔ. Jūn zǐ jū zé guì zuǒ, yòng bīng zé guì yòu. Bīng zhě bù xiáng zhī qì, fēi jūn zǐ zhī qì, bù dé yǐ ér yòng zhī, tián dàn wéi shàng. Shèng ér bù měi, ér měi zhī zhě, shì lè shā rén. Fú lè shā rén zhě, zé bù kě dé zhì yú tiān xià yǐ. Jí shì shàng zuǒ, xiōng shì shàng yòu. Piān jiāng jūn jū zuǒ, shàng jiāng jūn jū yòu, yán yǐ sāng lǐ chǔ zhī. Shā rén zhī zhòng, yǐ bēi āi qì zhī; Zhàn shèng yǐ sāng lǐ chǔ zhī.

Weapons are instruments of ill omen; all creatures loathe them. Therefore those who hold the Tao do not dwell with them. In ordinary life the noble person honors the left; in military affairs the right is honored. Weapons are instruments of ill omen, not the tools of a noble person. They are used only when there is no choice, and even then restraint and calm are highest. Even in victory, there is nothing to celebrate — to celebrate victory is to delight in the killing of people. One who delights in killing cannot achieve his purpose in the world. In auspicious matters, the left side is honored; in mourning matters, the right. The subordinate general stands on the left; the supreme general on the right — meaning they are conducted as if at a funeral. For the many who have been killed, weep for them with grief and sorrow. Even victory in war is to be treated as a funeral rite.

— Tao Te Ching 31

Source: Wang Bi edition (Chinese) + Hanyu Pinyin transliteration