《资治通鉴·唐纪·唐纪四十七》
颜真卿说： 老臣办事一无成绩，应当是死罪。不知使者是几时从长安出发的？ 
真卿曰： 老臣无状，罪当死，不知使者几日发长安？ 
Yan Zhenqing said: This old official has achieved nothing in his work, and deserves death. But I wonder when you, envoy, set out on your journey from Chang’an?