《北史·列传·卷七十四》
窦瑗十七岁时，就挟带书卷外出投师，求学十年，才做御史。
瑗年十七，便荷帙从师，游学十载，始为御史。
When Dou Yuan was seventeen years old, he took his books outside to study, and he studied for ten years before becoming an imperial historian.