《礼记·檀弓上》
朝奠在日出时举行，夕奠在太阳尚未落山时举行。父母死后，孝子一想到伤心之处就哭，是为了让父母的神魂能循着哭声回家。
父母之丧，哭无时，使必知其反也。
The morning sacrifice is held at sunrise, the dusk sacrifice is held before sunset. After their parents die, filial children cry out of grief whenever they think of their parents, so that their parents' spirits can find their way home by the sound of their crying.