《贞观政要·卷三·论择官》
贞观十一年，治书侍御史刘洎认为尚书左、右丞的人选应当特别精心挑选，上疏说： 臣知道尚书省日理万机，是施政的中枢，这里人员的选用任命，确实很不简单。
贞观十一年，治书侍御史刘洎以为左右丞宜特加精简，上疏曰： 臣闻尚书万机，实为政本，伏寻此选，授任诚难。
In the eleventh year of Zhenguan, Liu Ji, the Minister of Writing and Shi Yu Shi, believed that the selection of the left and right servants of Shangshu should be particularly meticulous, and said in the memorial: I know that the Shangshu Province has to deal with thousands of things every day and is the central hub of the government. The selection and appointment of personnel here is indeed not simple.