俱舍論疏 21.62

21.62

論「疑憂相應至心愁慼故」，釋疑，受相應也。疑心猶豫求決定智，正疑之時於境不決，故生憂慼。

On the passage in the treatise, "Doubt is associated with sorrow ... because the mind is grieved": this explains the association of doubt with feelings. A doubtful mind is hesitant and seeks determinate knowledge; when actively doubting, it is undecided regarding the object, and therefore sadness and grief arise.