《资治通鉴·隋纪·隋纪六》
但恐怕唐告诉了东都守备，东都事先进行了固守的准备，要是率兵进攻东都，百日内攻城不下，全国各地的军队四面八方地到来，其结果就不是我所能预料的了。 杨玄感说： 不对。
但恐唐祎告之，先己固守。若引兵攻之，百日不克，天下之兵四面而至，非仆所知也。 
But I am afraid that Tang has informed the defenders of the Eastern Capital, and the Eastern Capital has made preparations for defense in advance. If we lead troops to attack the Eastern Capital, the city will not be captured within a hundred days. The troops from all over the country will come from all directions. The result is beyond my expectations. Yang Xuangan said: No.