《旧唐书·本纪·卷十五》
九月三十日，皇上顾视着宰臣们说： 朕读《玄宗实录》，见开元初年时玄宗锐意追求治理国家，至开元十六年以后，似乎逐渐松懈倦怠，开元末年又不及中期，这是什么原因呢？ 
乙巳，上顾谓宰臣曰： 朕读《玄宗实录》，见开元初锐意求理，至十六年已后，稍似懈倦，开元未又不及中年，何也？ 
On the thirtieth day of the ninth lunar month, the emperor looked at the ministers and said: I have read the "Records of Emperor Xuanzong", and I saw that in the early years of Kaiyuan, Emperor Xuanzong was very enthusiastic about governing the country. After sixteen years of Kaiyuan, it seemed to gradually relax and become tired. The end of the Kaiyuan dynasty was not as good as the middle period. What is the reason for this?