俱舍論記 25.18

25.18

「若執退者至故唯有二」者，敘異執破。若執前五必退等者，於欲界中可具六種。於上二界應唯有二，安住、不動，無餘四種。彼無退失故，無退種姓；彼無自害故，無思種姓；彼無自防故，無護種姓；彼無練根故，無堪達種姓，故唯有二。

Regarding "If one insists that falling away ... therefore there are only two": this sets forth and refutes a divergent view. If one insists that the preceding five must fall away and so forth, then in the desire realm all six kinds could be present. But in the upper two realms there should be only two—abiding and immovable—without the other four. Since there is no falling away there, there would be no falling-away lineage; since there is no killing oneself there, there would be no deliberating lineage; since there is no guarding oneself there, there would be no guarding lineage; since there is no training of faculties there, there would be no capable-of-advancement lineage; therefore there would be only two.