《论衡·卷二十八·书解篇》
回答说：周文王忙得到太阳偏西了还没有空去吃饭，这是为推演《易》和增加卦数。
答曰：文王日昃不暇食，此谓演《易》而益卦。
It is said: King Wen of Zhou was so busy that he had no time to eat even when the sun was setting, this is because he was developing the I Ching and increasing the number of hexagrams.