《隋书·列传·卷十六》
长孙晟和他一起游猎，因便考察山川形势、部众强弱，全都知道了。
晟与之游猎，因察山川形势，部众强弱，皆尽知之。
Changsun Sheng went hunting with him and thereby surveyed the terrain of mountains and rivers and the strengths of the tribesmen, learning all about them.