《北史·列传·卷八十七》
可汗一直住在于都斤山，牙帐门朝东开，大概是敬重太阳升起的地方的缘故。
可汁恆处于都斤山，牙帐东开，盖敬日之所出也。
The Khan always lived in Yidujinshan Mountain, and the main tent door opened to the east, probably because he respected the place where the sun rises.