《新唐书·列传·卷一百四十八》
在他母丧期间，初一十五都给哭假，他就微服与杜元纪去郊野登高窥察灾气，众人怀疑他将有异图。
居母丧，朔望给告，即羸服与元纪出野，冯高窥觇灾眚，众疑其有异谋。
During his mother's mourning period, he was given a mourning leave on the first and fifteenth day of each month, so he went to the countryside in disguise with Du Yuanji to climb high and observe the signs of disaster. Many people suspected that he had ulterior motives.