《北史·列传·卷八十六》
母牛趴下不能前行，别部的人教给他们用犍牛替代母牛，蠕蠕说： 它的母亲尚不能行走，何况那个儿子？ 
异部人有教其以犍牛易之来者，蠕蠕曰： 其母尚不能行，而况其子！ 
When a heifer lay down and could not move forward, people from other tribes taught them to use oxen instead of heifers, but Rouran people said: If its mother can't walk, how can its son?