佛祖歷代通載 12.55

12.55

（乙酉）　改垂拱○制母齊縗。古者母亡朞年而已。喪服篇云。天無二日。士無二主。國無二君。家無二尊。以一制朞年禮也。自天皇上元元年。天后表請。父在為母三年。下詔依行。至今垂拱始編入格。

(Yiyou [685 CE]) The era was changed to Chuigong. ○ The mourning grade of trimmed sackcloth (qicui) was instituted for mothers. In ancient times, the mourning period on the death of a mother was only one full year. The "Mourning Attire" chapter [of the Yili] states: "Heaven has no two suns; a scholar has no two masters; a state has no two rulers; a household has no two heads of family." By this single principle, a one-year mourning period was prescribed by ritual. Starting from the first year of Tianhuang's Shangyuan era, the Empress of Heaven submitted a memorial requesting that mourning for a mother while the father is still alive should last three years. An imperial edict was issued approving its implementation. Only now in Chuigong was it first codified into law.