成唯識論掌中樞要 2.115

2.115

論中不通一切識身者，意地一切根相應者。既說根言，如何可證意有苦根？答：前說俱生一切煩惱皆於三受現行可得，故知根者，即是苦根。

In the treatise, what does not pervade all consciousness-bodies is that which is associated with all faculties of the manas-plane. Since it speaks of the word "faculty," how can it be proven that the manas possesses the faculty of pain? Answer: It was previously said that all innate afflictions can be found operating in the three feelings; hence we know that the "faculty" is precisely the faculty of pain.