《战国策·秦二·秦王谓甘茂》
秦王对甘茂说： 楚国使者大都能言善辩，与寡人争论时让我多次理屈辞穷，有什么办法对付他们呢？ 
秦王谓甘茂曰： 楚客来使者多健，与寡人争辞，寡人数穷焉，为之奈何？ 
King Qin said to Gan Mao: The envoys of the state of Chu are all eloquent and good at arguing. They have made me unable to reason with them many times. What can I do to deal with them?