《资治通鉴·唐纪·唐纪四》
李世勣又派人劝窦建德说： 曹、戴二州，户口充实，孟海公占据二州，与东都的郑国貌合神离，如果发大军进取二州，指日可待。
李世勣复遣人说窦建德曰： 曹、戴二州，户口完实，孟海公窃有其地，与郑人外合内离；若以大军临之，指期可取。
Li Shiji sent someone to persuade Dou Jiande again, saying: Cao and Dai prefectures are densely populated. Meng Haigong occupies the two prefectures and seems to be at odds with Zheng Guo of the Eastern Capital. If a large army is sent to attack the two prefectures, it will not be very long before they are conquered.