《论衡·卷十三·效力篇》
颜渊，已曾在德行的 路 上超过了孔子，弄得精疲力尽，发白齿落。
颜氏之子，已曾驰过孔子於涂矣，劣倦罢极，发白齿落。
Yan Yuan had already surpassed Confucius on the path of virtue, making himself exhausted, his hair turned white and his teeth fell out.