Mencius - Book 3, Part 2, Chapter 6

Mencius said to Tâi Pû-shang, 'I see that you are desiring your king to be virtuous, and will plainly tell you how he may be made so. Suppose that there is a great officer of Ch'û here, who wishes his son to learn the speech of Ch'î. Will he in that case employ a man of Ch'î as his tutor, or a man of Ch'û?' 'He will employ a man of Ch'î to teach him,' said Pû-shang.

Mencius went on, 'If but one man of Ch'î be teaching him, and there be a multitude of men of Ch'û continually shouting out about him, although his father beat him every day, wishing him to learn the speech of Ch'î, it will be impossible for him to do so. But in the same way, if he were to be taken and placed for several years in Chwang or Yo, though his father should beat him, wishing him to speak the language of Ch'û, it would be impossible for him to do so.

'You supposed that Hsieh Chü-châu was a scholar of virtue, and you have got him placed in attendance on the king. Suppose that all in attendance on the king, old and young, high and low, were Hsieh Chü-châus, whom would the king have to do evil with? And suppose that all in attendance on the king, old and young, high and low, are not Hsieh Chü-châus, whom will the king gave to do good with? What can one Hsieh Chü-châu do alone for the king of Sung?'
~ James Legge translation via nothingistic.org ~

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