《汉书·志·律历志下》
所以《洛诰》篇上就说： 戊辰，王在新邑，祭祀岁，命作策，周公辅佐文王、武王受天命，有七年。 
故《洛诰》篇曰： 戊辰，王在新邑，祭岁。命作策，惟周公诞保文、武受命，惟七年。 
Therefore, in the "Luo Gao", it says: On Wuwu, the king was in Xinyi. During the sacrifice to Sui, he ordered Zuo Ce to be written. And Zhou Gong assisted King Wen and King Wu in following the mandate of heaven for seven years.