瑜伽論記 9.100

9.100

由無二故，說名中道遠離二邊，亦名無上者，由無二種義故即是遠離增損二邊，得稱中道，故亦名無上。

Regarding "Because it is non-dual, it is called the middle path, free from the two extremes, and is also called unsurpassable": because it is devoid of the two kinds of meaning, it is free from the two extremes of superimposition and deprecation, thereby gaining the designation "middle path"; hence it is also called unsurpassable.