《旧唐书·列传·卷四》
听说唐用全部兵力攻打王世充，连头连尾两年时间，郑的形势一天比一天紧急，而唐的围攻毫不放松。
闻唐兵悉众攻郑，首尾二年，郑势日蹙而唐兵不解。
It is said that Tang army attacked Wang Shichong with the whole force, for two years long, Zheng's situation was getting more and more urgent, Tang's siege was never relieved.