《明史·志·卷六十七》
二十一年，敕令各边的军士，每年九月到第二年三月，都要经常操练，仍然要把操练过的军马以及有风雪停止操练的时日情况奏报。
二十一年，敕各边军士，每岁九月至明年三月，俱常操练，仍以操过军马及风雪免日奏报。
In the twenty-first year, the soldiers of each side were ordered to conduct regular drills every year from September to March of the following year, and to report on the horses that had been trained for drills as well as the times when drills were suspended due to snow and wind.