元朝秘史
Although this defeat left the Rus' principalities at the mercy of invaders, the Mongol or Tartar forces retreated and did not reappear for thirteen years, during which time the princes of Rus' went on quarreling and fighting as before, until they were startled by a new and much more formidable invading force. In The Secret History of the Mongols, the only reference to this early battle is: