Mencius - Book 5, Part 2, Chapter 4D

Chang urged, 'Then are we to suppose that when Confucius held office, it was not with the view to carry his doctrines into practice?' 'It was with that view,' Mencius replied, and Chang rejoined, 'If the practice of his doctrines was his business, what had he to do with that struggling for the captured game?'

Mencius said, 'Confucius first rectified his vessels of sacrifice according to the registers, and did not fill them so rectified with food gathered from every quarter.' 'But why did he not go away?' He wished to make a trial of carrying his doctrines into practice. When that trial was sufficient to show that they could be practiced and they were still not practiced, then he went away, and thus it was that he never completed in any State a residence of three years.

'Confucius took office when he saw that the practice of his doctrines was likely; he took office when his reception was proper; he took office when he was supported by the State. In the case of his relation to Chî Hwan, he took office, seeing that the practice of his doctrines was likely. With the duke Ling of Wei he took office, because his reception was proper. With the duke Hsiâo of Wei he took office, because he was maintained by the State.'
~ James Legge translation via nothingistic.org ~

Go here to read the introductory post to this serialized version of the Works of Mencius.