俱舍論頌疏論本 28.57

28.57

染由生及退者，染污等至由二緣得：一、由受生，謂從上地生下地時，得下地染；二者，由退，謂於此地離染退時，得此地染。

As for 'the defiled, through birth and falling away,' the defiled samāpatti is acquired through two conditions: first, through taking rebirth, meaning that when born from a higher stage into a lower stage, one acquires the defilement of the lower stage; second, through falling away, meaning that when one falls away from dispassion regarding this stage, one acquires the defilement of this stage.