《史记·八书·历书》
帝王受天命而改朝换代，对于开始必十分慎重，所以要更改历法，改变服装崇尚的颜色，推算历法的起始点历元，以顺承天的意旨。
王者易姓受命，必慎始初，改正朔，易服色，推本天元，顺承厥意。
Emperors, upon receiving the mandate of heaven, and establishing new dynasties, must be very careful in the beginning, so it is necessary to renew the calendar, to renew one's attire and robes, to seek out the true beginning point of the calendar, in order to conform to the will of heaven.