《史记·七十列传·韩长孺列传》
于是暗中派遣聂翁壹做间谍，逃到匈奴，对单于说： 我能杀死马邑城的县令县丞等官吏，将马邑城献给您投降，财物可以全部得到。 
阴使聂翁壹为间，亡入匈奴，谓单于曰： 吾能斩马邑令丞吏，以城降，财物可尽得。 
So they secretly sent Nie Wuyi to be a spy, he went to the Xiongnu and told the Chanyu: I can kill all the officials in Mayi city including the county magistrate, and surrender Mayi city to you, all the wealth can be yours. 