瑜伽師地論略纂 2.18

2.18

根二因不壞：一、不滅壞故，非全無；二、不羸劣故，非劣弱。五十四中釋滅壞、羸劣及由四緣諸根變異，翻彼即是此中二義。此說色根。其意根不壞者，彼說由四緣意根壞，翻彼即是。彼意根，第六是，不同五根。不說七八根不壞義，思准可知。

The faculties are undamaged due to two causes: first, because they are not destroyed, they are not completely absent; second, because they are not emaciated and weak, they are not deficient and feeble. The explanation in fascicle 54 of destruction, emaciation, and the alteration of the faculties due to four conditions is the reverse of these two meanings here. This refers to the physical faculties. As for the mental faculty being undamaged, it is the reverse of that text's explanation of the mental faculty being damaged due to four conditions. That mental faculty is the sixth [consciousness], unlike the five faculties. That it does not speak of the seventh and eighth faculties being undamaged can be known by inference.