《旧唐书·本纪·卷二》
再说始毕可汗全国的军队敢于包围天子，必定是认为国家仓猝之间无人救援。
且始毕可汗举国之师，敢围天子，必以国家仓卒无援。
To put it another way, if the army of Shibikhan dared to surround the emperor, it must have thought that the country had no reinforcements in a hurry.