Mencius - Book 3, Part 1, Chapter 4F

'I have heard of men using the doctrines of our great land to change barbarians, but I have never yet heard of any being changed by barbarians. Ch'an Liang was a native of Ch'û. Pleased with the doctrines of Châu-kung and Chung-nE, he came northwards to the Middle Kingdom and studied them. Among the scholars of the northern regions, there was perhaps no one who excelled him. He was what you call a scholar of high and distinguished qualities. You and your brother followed him some tens of years, and when your master died, you forthwith turned away from him.

'Formerly, when Confucius died, after three years had elapsed, his disciples collected their baggage, and prepared to return to their several homes. But on entering to take their leave of Tsze-kung, as they looked towards one another, they wailed, till they all lost their voices. After this they returned to their homes, but Tsze-kung went back, and built a house for himself on the altar-ground, where he lived alone other three years, before he returned home.

'On another occasion, Tsze-hsiâ, Tsze-chang, and Tsze-yû, thinking that Yû Zo resembled the sage, wished to render to him the same observances which they had rendered to Confucius. They tried to force the disciple Tsang to join with them, but he said, "This may not be done. What has been washed in the waters of the Chiang and Han, and bleached in the autumn sun: how glistening is it! Nothing can be added to it."
~ James Legge translation via nothingistic.org ~

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