《资治通鉴·隋纪·隋纪四》
元德太子杨昭从长安来朝见炀帝，几个月后要返回长安。
元德太子昭自长安来朝，数月，将还，欲乞少留；帝不许。
Crown Prince Yang Zhao of Yuande came from Chang'an to have an audience with Emperor Yang and wanted to return to Chang'an after several months.