at Xi Prefecture, he, under the guise of a hunting party, summoned a number of tribal chiefs loyal to Tang in the area, and once they arrived, launched a surprise attack on Ashina Duzhi, who, caught by surprise, was forced to surrender; Li Zhefu then surrendered as well. (Narsieh, having been used in this manner, was left in the region to fend for himself.) Meanwhile, though, another trouble was flaring up for Tang. The former Göktürk territory, over which Tang had established 24 prefectures with the tribal chiefs serving as prefects, rebelled, and, under the leadership of Ashide Wenfu () and Ashide Fengzhi (), supported Ashina Nishoufu as khan. Emperor Gaozong sent Xiao Siye to attack Ashina Nishoufu, but after Xiao achieved a few victories, he became careless, and a counterattack by Ashina Nishoufu crushed him, advancing as far as Ding Prefecture. Ashina Nishoufu also encouraged the Xi and the Khitan to attack Ying Prefecture (營州, roughly modern Zhaoyang, Liaoning), although those attacks were fought off. Around the new year 680, after Pei returned from the Western Turkic Khaganate front, Emperor Gaozong commissioned him to attack the Göktürks. Pei defeated and captured Ashide Fengzhi, and Ashina Nishoufu's subordinates killed him and surrendered, ending the rebellion. Meanwhile, Li Xian's relationship with Empress Wu was deteriorating, as Li Xian heard rumors that he was not born of Empress Wu but her sister Lady of Han, and was fearful. Meanwhile, earlier, Ming Chongyan (), a sorcerer trusted by Empress Wu and Emperor Gaozong, had repeatedly stated that he believed Li Xian did not have the abilities to be emperor, that his younger brother Li Zhe the Prince of Ying had an appearance like Emperor Taizong, and that another younger brother, Li Dan the Prince of Xiang, had the most honored appearance of all. Knowing that Li Xian was fearful of her, Empress Wu had the North Gate Scholars author teachings on filial piety to give to Li Xian, and also personally rebuked him, further causing him to be alarmed. When Ming was assassinated in 679, Empress Wu suspected Li Xian of carrying out the assassination. She had a report made to Emperor Gaozong that accused Li Xian of assassinating Ming. When the officials Xue Yuanchao, Pei Yan, and Gao Zhizhou were put in charge of investigations, they discovered a number of armors in Li Xian's palace. Empress Wu thus accused Li Xian of