《资治通鉴·晋纪·晋纪二》
太子外出则从君出征，守在国都之内是在君王外出时代行处理国政，不能说没有事情可作，所以太子应当哭别之后，除去丧服，居丧三年。 
太子出则抚军，守则监国，不为无事，宜卒哭除衰麻，而以谅闇终三年。 
When the crown prince went out, he followed the gentleman to battle; when he remained within the capital, he handled state affairs in the stead of the gentleman when the gentleman was away. It cannot be said that there was nothing to do, therefore the crown prince should, after the appropriate mourning, remove the mourning clothes, and observe mourning for three years.