資治通鑑
The "ambush" mentioned in the "Sanguozhi" refers to the ambush that Lü Bu's forces fell into on the second day, as described in the "Wei Shu". The incident is also mentioned in Sima Guang's "Zizhi Tongjian". However, the "Zizhi Tongjian" account, which combined the "Sanguozhi" and "Wei Shu" accounts, did not mention the events on the first day – about Cao Cao sending all his available soldiers to defend the base and ordering women to stand guard on the walls.