《隋书·列传·卷二十一》
周武帝遭太后之丧，却与左右出去打猎。张衡免冠露发，抓住武帝的坐骑，直言劝谏。
周武帝居太后忧，与左右出猎，衡露发舆榇，扣马切谏。
When Emperor Wu of Zhou was mourning the death of his empress dowager, he went hunting with his entourage. Zhang Heng took off his hat and exposed his hair. He grabbed Emperor Wu's mount and directly advised him.