Tao Te Ching 31

Now arms, however beautiful, are instruments of evil omen, hateful, it may be said, to all creatures. Therefore they who have the Tao do not like to employ them.

The superior man ordinarily considers the left hand the most honorable place, but in time of war the right hand. Those sharp weapons are instruments of evil omen, and not the instruments of the superior man—he uses them only on the compulsion of necessity. 

Calm and repose are what he prizes; victory by force of arms is to him undesirable. To consider this desirable would be to delight in the slaughter of men, and he who delights in the slaughter of men cannot get his will in the kingdom.

On occasions of festivity to be on the left hand is the prized position; on occasions of mourning, the right hand. 

The second in command of the army has his place on the left; the general commanding in chief has his on the right—his place, that is, is assigned to him as in the rites of mourning. 

He who has killed multitudes of men should weep for them with the bitterest grief, and the victor in battle has his place rightly according to those rites.