《汉书·传·李广苏建传》
公孙敖军无功而回，说： 捕到的俘虏说：李陵教单于用兵以防备汉军，因此臣无所获。 
敖军无功还，曰： 捕得生口，言李陵教单于为兵以备汉军，故臣无所得。 
Gongsun Ao's army returned without success, saying, "The captured prisoners said: Li Ling taught the Chanyu how to use troops to defend against the Han army, so there was nothing for me to achieve."