俱舍論疏 17.29

17.29

論「若作是說至名斷善根」，引本論證九品斷善正也。既有最後所捨者，亦有前品捨者，故知非一品斷。

On the Śāstra's stating: "If it is explained thus [...] is called the severance of wholesome roots", this cites the root treatise to prove that the severance of wholesome roots in nine grades is correct. Since there are those abandoned at the very end, there must also be those abandoned in preceding grades; hence one knows that they are not severed in a single grade.