《汉书·传·傅常郑甘陈段传》
后来束莱郡有黑龙在冬天裹出现，有人就问陈汤，陈汤说： 这是所谓的玄门开启。
后东莱郡黑龙冬出，人以问汤，汤曰： 是所谓玄门开。
Later, a black dragon appeared in winter in Shule County, and someone asked Chen Tang. Chen Tang said: This is the so-called "Xuanmen" opening.