Mencius. Book 2, Part 2, Chapter 13.
Book 2, Kung-Sun Ch'ow. Part 2.
1. When Mencius left Ts'e, Ch'ung Yu questioned him upon the way, saying, "Master, you look like one who carries an air of dissatisfaction in his countenance. But formerly I heard you say ‹ 'The superior man does not murmur against Heaven, nor grudge against men.' "
2. Mencius said, "That was one time, and this is another.
3. "It is a rule that a true imperial sovereign should arise in the course of five hundred years, and that during that time there should be men illustrious in their generation.
4. "From the commencement of the Chow dynasty till now, more than 700 years have elapsed. Judging numerically, the date is past. Examining the character of the present time, we might expect the rise of such individuals in it.
5. "But Heaven does not yet wish that the empire enjoy tranquillity and good order. If it wished this, who is there besides me to bringit about? How should I be otherwise than dissatisfied?
Text source: The Works of Mencius. Translated by James Legge.