《论衡·卷三·物势篇》
天有苍龙、白虎、朱鸟、玄武 四星 的精气，所以在地上造就出龙、虎、鸟、龟 四兽 的身体。
北方，水也，其星玄武也。天有四星之精，降生四兽之体。
The heaven has the vital energy of four stars including the green dragon, white tiger, red bird and black tortoise, so it creates the bodies of four animals including dragon, tiger, bird and turtle on the ground.