《旧唐书·列传·卷九十三》
相持很久，录事参军李宇为程华谋划道： 使君长年遭受围困，张尚书不能前来救援，论功献捷，须到定州之后，现在这样就是所谓劳而无功了。
久之，录事参军李宇为华谋曰： 使君受围累年，张尚书不能致援，论功献捷，须至中山，所谓劳而无功者也。
The stalemate lasted for a long time, and Li Yu, the military attaché, planned for Cheng Hua: "Your Excellency has been under siege for a long time, and Minister Zhang cannot come to rescue you. Judging from your merits, you must go to Dingzhou, and this will be a so-called fruitless labor."