瑜伽論記 14.187

14.187

下釋所以者何乃至一切煩惱者，貪等煩惱畢竟不淨，非煩惱故不得言畢竟不淨，此據相續道中捨有漏識得無漏識，以同非煩惱故亦不獨為煩惱因緣。

Below, it explains "why is this?... up to... all afflictions": afflictions such as covetousness are utterly impure; because [consciousness] is not an affliction, it cannot be said to be utterly impure. This is based on relinquishing tainted consciousness and obtaining taintless consciousness in the path of succession; because it is equally not an affliction, it also does not solely act as the cause and condition for afflictions.