《逸周书·卷六·月令解》
立夏前三天，太史向天子禀告说； 某日立夏，大德在于火。 天子于是斋戒，准备迎夏。
先立夏三日，太史谒之天子，曰：某日立夏，盛德在火，天子乃齐。
Three days before the Lixia, the grand historian reported to the emperor: The Lixia will be on a certain day, and the virtue is in fire. The emperor then fasted and prepared to welcome the summer.