Mencius - Book 2, Part 2, Chapter 8

Shan T'ung, on his own impulse, asked Mencius, saying, 'May Yen be smitten?' Mencius replied, 'It may. Tsze-k'wâi had no right to give Yen to another man, and Tsze-chih had no right to receive Yen from Tsze-k'wâi. Suppose there were an officer here, with whom you, Sir, were pleased, and that, without informing the king, you were privately to give to him your salary and rank; and suppose that this officer, also without the king's orders, were privately to receive them from you would such a transaction be allowable? And where is the difference between the case of Yen and this?'

The people of Ch'î smote Yen. Some one asked Mencius, saying, 'Is it really the case that you advised Ch'î to smite Yen?' He replied, 'No. Shan T'ung asked me whether Yen might be smitten, and I answered him, "It may." They accordingly went and smote it. If he had asked me "Who may smite it?" I would have answered him, "He who is the minister of Heaven may smite it." Suppose the case of a murderer, and that one asks me "May this man be put to death?" I will answer him "He may." If he ask me "Who may put him to death?" I will answer him, "The chief criminal judge may put him to death." But now with one Yen to smite another Yen: how should I have advised this?'
~ James Legge translation via nothingistic.org ~

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