《资治通鉴·后周纪·后周纪二》
杨衮驱马向前观望北周军队，退下来对北汉主说： 是劲敌啊，不可轻易冒进！ 
杨兗策马前望周军，退谓北汉主曰： 勍敌也，未可轻进！ 
Yang Gun spurred his horse forward to observe the Northern Zhou army. He came back and said to the Northern Han emperor: They are a formidable enemy! We should not attack rashly!