俱舍論記 3.131

3.131

「以無樂根至極堅牢故」者，答。以無第三靜慮樂根證不還果，而於後時得有退義。以樂證果必是超越，夫超越人必無退義。亦無次第人退已由樂復得，以樂依第三定故。夫次第人，無間道依未至定捨受相應，解脫道或未至定捨受相應，或入根本喜受相應，證不還果。必無退已由樂復得故，無一人具用三受故，不可說十一根得。雖超越人或喜、或捨，證不還果，亦無退義。若次第者，以喜、捨證，則容有退。是則喜、捨不定，樂根即決定不退，故偏說樂。若用樂根得果者，必無復用喜、捨根得。若用喜、捨得者，亦無由樂復得。若據轉根，亦容樂得。今據從向得果，唯論初得，故不說彼也。非先離欲界超越證第三果有還退義，此離欲不還果二道所得極堅牢故，一先以世間道得、二後以出世道得，此顯超越不還不退也。若次第證，無二道重得義，故容有退。其第四果唯次第得，無超越證義，故容數退。

"Because without the faculty of pleasure... extremely solid": this is the answer. Because there is no case where one realizes the fruit of the non-returner through the faculty of pleasure of the third dhyāna and at a later time has the fact of falling away. Realizing the fruit through pleasure must be done by direct leap (vyutkrāntaka); and one who leaps directly definitely never has the fact of falling away. Nor is there any gradual person who, having fallen away, attains it again through pleasure, because pleasure is based on the third dhyāna. A gradual person has an uninterrupted path based on the preparatory stage associated with the sensation of equanimity, and a path of liberation either based on the preparatory stage associated with the sensation of equanimity, or entering the fundamental stage associated with the sensation of joy, to realize the fruit of the non-returner. Because it is definitely never the case that, having fallen away, one attains it again through pleasure, no single person completely uses the three sensations; therefore, it cannot be said to be attained by eleven faculties. Although a person who leaps directly may realize the fruit of the non-returner through joy or through equanimity, neither do they ever fall away. If it is a gradual person, realizing it through joy or equanimity, it is then possible to fall away. Thus, joy and equanimity are not fixed, whereas the faculty of pleasure is definitely without falling away; hence [the treatise] mentions pleasure specifically. If one attains the fruit using the faculty of pleasure, one definitely never attains it again using the faculties of joy or equanimity. If one attains it using joy or equanimity, one also never attains it again through pleasure. If it were based on transforming the faculties, it would also be possible to attain it through pleasure. Here it is based on attaining the fruit from the path of progress and discusses only the initial attainment; thus it does not speak of that. It is not that one who had previously detached from the desire realm and directly leaped to realize the third fruit could ever fall away, because this non-returner fruit detached from desire is attained by the two paths and is extremely solid: first, it was attained by the worldly path; second, it was subsequently attained by the supramundane path. This shows that the leaping non-returner does not fall away. If it is realized gradually, there is no repeated attainment by the two paths; therefore falling away is possible. The fourth fruit is attained only gradually and is never realized by leaping directly; therefore repeated falling away is possible.