俱舍論頌疏論本 25.7

25.7

釋曰：退法種姓必是先有，思法等五亦有後得。謂有先來是思法姓，或有從退練根成思，乃至不動法，如思法說。此中退法非必定退，乃至堪達非必能達，但約容有，建立此名，故六阿羅漢通三界皆有。若退定退、堪達定達，是則上界唯有安住、不動二種，闕餘四也。謂彼上界無有退失、自害、自防及練根故，故無餘四。

Explanation: The lineage of falling-away dharma must be originally possessed; the five beginning with thinking dharma may also be subsequently obtained. That is, some are originally of the thinking dharma lineage, while others hone their faculties from falling-away to become thinking [dharma], and so on up to unshakeable dharma, just as explained for thinking dharma. Here, falling-away dharma does not necessarily mean one definitely falls away, nor does capable of penetration definitely mean one is able to penetrate; this designation is established merely on the basis of possibility. Therefore, the six arhats exist across all three realms. If the falling-away definitely fell away and the capable of penetration definitely penetrated, then the higher realms would only have two kinds—abiding and unshakeable—lacking the other four. That is because those higher realms lack falling away and loss, harming oneself, guarding oneself, and honing faculties, and therefore lack the remaining four.