俱舍論記 21.42

21.42

「疑憂相應至必住捨受」者，疑憂相應，慼行轉故。非喜相應，非歡行故。唯意地故，憂根相應。非五識故，非苦相應。求決定知，心愁慼故，所以非歡行轉。餘四見、慢，與喜相應，歡行轉故。非憂相應，非慼行故。唯意地故，喜根相應。非五識故，非樂相應。已約別相說諸煩惱與受相應，就通相說受相應者，一切煩惱皆捨受相應，以諸隨眠相續斷位，勢力衰歇必住捨受。以捨處中，不違歡、慼，故遍相應。

On the phrase “Doubt is associated with dejection… must abide in neutral feeling”: Doubt is associated with dejection because it operates in a sorrowful mode. It is not associated with joy because it does not operate in a joyous mode. Because it belongs only to the mental plane, it is associated with the dejection faculty. Because it does not belong to the five consciousnesses, it is not associated with pain. Because the mind is sorrowful when seeking determinate knowledge, it does not operate in a joyous mode. The remaining four views and pride are associated with joy, because they operate in a joyous mode. They are not associated with dejection, because they do not operate in a sorrowful mode. Because they belong only to the mental plane, they are associated with the joy faculty. Because they do not belong to the five consciousnesses, they are not associated with pleasure. Having explained the association of the defilements with feelings according to specific characteristics, when speaking of association with feelings according to common characteristics: all defilements are associated with neutral feeling (upekṣā), because when the continuity of the anuśayas is cut off, their power declines and they necessarily abide in neutral feeling. Since neutrality is intermediate and does not conflict with joy or sorrow, it is universally associated.