Yong-le: Year 4, Month 5, Day 17
3 Jun 1406
The Emperor noted that, as Che-li and other pacification superintendencies and Meng-ding, Wan Dian and other prefectures and subprefectures in Yun-nan were coming to offer tribute every year, and he was concerned because the roads were dangerous and long, that they should only be required to offer tribute once every three years and were to be advised of this through orders. This regulation was not however to apply to the sending of envoys to express congratulations or to express gratitude for Imperial grace.
Zhong-yang Yan-jiu yuan Ming Shi-lu, volume 11, page 806