《礼记·月令》
立秋前三天，太史察告天子说： 某日立秋，金德当令。 
先立秋三日，大史谒之天子曰：某日立秋，盛德在金。
Three days before Start of Autumn, the Imperial Astronomer notifies the Son of Heaven and says: Start of Autumn falls on a certain day, and the Virtue of Metal shall commence.