《资治通鉴·唐纪·唐纪二十五》
李成器推辞道： 国泰民安则应当先立嫡长子，国家多难则应当首先将有功的人立为太子；如果在这个问题上违反时宜，就会让普天之下的人大失所望。
成器辞曰： 国家安则先嫡长，国家危则先有功；苟违其宜，四海失望。
Li Chengqi declined, saying: "If the country is peaceful and the people live in peace, it is appropriate to firstly establish a legitimate heir; if the country is facing huge troubles, it is appropriate to firstly establish a person with great contributions as the crown prince. If the timing of this matter is violated, common people would be very disappointed.