《资治通鉴·晋纪·晋纪二十三》
前秦王苻坚听说慕容恪去世，暗地里炮制了图谋前燕的计策，想看看这个计策是否可行，就命令匈奴右贤王曹毂启程出使前燕进献贡奉，以西戎主簿郭辩作他的副手。
秦王坚闻恪卒，阴有图燕之计，欲觇其可否，命匈奴曹毂发使如燕朝贡，以西戎主簿冯翊郭辩为之副。
Emperor Fu Jian of Former Qin heard that Murong Ke had died, and he secretly plotted to make a raid on Former Yan. To see if his plot would succeed, he ordered Cao Gu the Right Wise King of the Xiongnu to depart on a mission to Former Yan to offer tribute, with Guo Bian the Registrar-in-chief of the Xiongnu serving as his assistant.