Mencius - Book 4, Part 2, Chapter 31B

When Tsze-sze was living in Wei, there came a band from Ch'î to plunder. Some one said to him, 'The plunderers are coming; why not leave this?' Tsze-sze said, 'If I go away, whom will the prince have to guard the State with?'

Mencius said, 'The philosophers Tsang and Tsze-sze agreed in the principle of their conduct. Tsang was a teacher; in the place of a father or elder brother. Tsze-sze was a minister; in a meaner place. If the philosophers Tsang and Tsze-sze had exchanged places the one would have done what the other did.'
~ James Legge translation via nothingistic.org ~

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