《资治通鉴·唐纪·唐纪六十九》
任命嗣曹王李龟年为宗正少卿充当使臣，任命徐云虔为副使，另外还派遣宦官中使随同，一道带着书信前往南诏。
以嗣曹王龟年为宗正少卿充使，以徐去虔为副使，别遣内使，共赍诣南诏。
He appointed Prince Li Guinian of Sicao to be the Junior Minister of the Department of Imperial Clan Affairs and to serve as an emissary, and appointed Xu Yunqian as his deputy. He also sent eunuchs to accompany them, and they all headed for Nanzhao with the letter. 