Mencius - Book 3, Part 1, Chapter 4G

'Now here is this shrike-tongued barbarian of the south, whose doctrines are not those of the ancient kings. You turn away from your master and become his disciple. Your conduct is different indeed from that of the philosopher Tsang.

'I have heard of birds leaving dark valleys to remove to lofty trees, but I have not heard of their descending from lofty trees to enter into dark valleys.

'In the Praise-songs of Lû it is said,

"He smote the barbarians of the west and the north,
He punished Ching and Shû."

Thus Châu-kung would be sure to smite them, and you become their disciple again; it appears that your change is not good.'
~ James Legge translation via nothingistic.org ~

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