《汉书·纪·成帝纪》
从古往今来的历史教训来看，祸乱的始生，多因继承人的问题而引起。
观于往古近事之戒，祸乱之萌，皆由斯焉。
Looking at the lessons of history from ancient times to the present, the beginning of chaos has often been caused by problems with the heir.