From 《
孔子家语·
观思》: '
薰莸不同器而藏,
尧桀不共国而治,
以其类异也' — 'fragrant and foul herbs are not stored in the same jar; Yao and Jie do not rule the same kingdom — because their kinds differ.'
薰 = fragrant herb;
莸 = a foul-smelling weed. Used to insist on moral separation.