《资治通鉴·唐纪·唐纪五十四》
当此之际，你要将全部兵马压向过境，号称攻打成德，但可以暗中给成德人送上一封书信说： 倘若魏博攻打成德，河北地区的仗义之士使会说魏博出卖朋友了；倘若魏博援助成德，河南地区的忠义之臣便会说魏博反叛君主了。
于是悉甲压境，号曰伐赵，而可阴遗赵人书曰： 魏若伐赵，则河北义士谓魏卖友；魏若与赵，则河南忠臣谓魏反君。
At this time, you should deploy all troops to the border, pretending to attack Chengde, but secretly send a letter to the Chengde people, saying: If Weibo attacks Chengde, the chivalrous people in Hebei will say that Weibo has betrayed its friends; if Weibo helps Chengde, the loyal ministers in Henan will say that Weibo has rebelled against its lord.