《汉书·纪·武帝纪》
二月，下诏说： 朕郊祭时见上天灵光，巡狩北边，见群鹤栖息，当时不是网罗捕杀之期，就没进行弋猎。
二月，诏曰： 朕郊见上帝，巡于北边，见群鹤留止，以不罗罔，靡所获献。
In February, an imperial edict was issued saying: When I offered sacrifices I saw divine light in the heaven. When I inspected the north, I saw a flock of cranes at rest. Since it was not the time for hunting with nets, I did not hunt them.