《荀子·不苟》
《诗》云： 该在左就在左，君子在左无不可；该在右就在右，君子在右也常有。 
《诗》曰： 左之左之，君子宜之；右之右之，君子有之。 
The Book of Odes says: When one should be on the left, one should be on the left, and there is nothing inappropriate for a gentleman to be on the left; when one should be on the right, one should be on the right, and it is also common for a gentleman to be on the right.