《明史·列传·卷六十六》
当初余子俊巡视宣府大同两镇，要求以延绥边墙法在两镇推行，因年成歉收而停止。
初，子俊巡历宣、大，请以延绥边墙法行之两镇，因岁歉而止。
In the past, when Yu Zixun inspected the two towns of Xuanfu and Datong, he requested to implement the method of border wall in Yansui in the two towns, but it was stopped due to poor harvests.