Chapter 2, Verses 17 and 18 - Sun Tzu

Therefore in chariot fighting, when ten or more chariots have been taken, those should be rewarded who took the first. Our own flags should be substituted for those of the enemy, and the chariots mingled and used in conjunction with ours. The captured soldiers should be kindly treated and kept. This is called, using the conquered foe to augment one's own strength.
~ from The Art of War, Giles translation ~

Go here to read the introductory post to the verses of The Art of War.