Yong-le: Year 19, Month 4, Day 12
13 May 1421
The Han-lin Academy Reader-in-waiting Li Shi-mian and the Expositor-in-waiting Zou Ji advised of matters beneficial to the people .... They also advised: "For successive years the tribute envoys from the man and the yi on the four sides have sought the Way through coming to Court. This has truly fatigued China. It should be clearly proclaimed to those abroad that, in coming to Court to offer tribute, the countries nearby should come once every three years and the distant countries should come once every five years. This will make things easier for both the officials and the people..."
Zhong-yang Yan-jiu yuan Ming Shi-lu, volume 14, page 2264/65