俱舍論頌疏論本 25.10

25.10

釋曰：不動種姓必無退理；就前五種，唯退法一，姓必不退，謂居下故。唯思法等四有種姓退，謂從思法退入退法，或從護法退入思法，或從安住退入護法，或從堪達退入安住，是名姓退。

Explanation: For the unshakeable lineage, there is certainly no possibility of falling away. Among the first five, falling-away dharma alone certainly does not fall away from lineage, because it occupies the lowest position. Only the four beginning with thinking dharma have falling away from lineage: that is, falling from thinking dharma into falling-away dharma; or falling from guarding dharma into thinking dharma; or falling from abiding into guarding dharma; or falling from capable of penetration into abiding. These are called falling away from lineage.