《明史·列传·卷二百一十五》
马匹分为三等，上等好马三十匹，收进皇帝的马房，其余的按等级给价，老瘠之马不要。
马分三等，上驷三十进御，余给价有差，老瘠者不入。
The horses were divided into three classes. Thirty of the best horses were collected into the royal stables, and the price of the remaining horses were set according to their class. The old and weak horses were not wanted.