大乘起信論義記 3.437

3.437

“Must also never follow the mind… nor subsequently eliminate mind with mind”: if there were real objects outside the mind, when the mind focuses on such objects it would be impossible to repress it from focusing; hence one would subsequently eliminate it with mind. Now, since there are no dust-objects outside the mind, the grasped is signless; and because the grasped is signless, the grasper naturally cannot arise—why activate a subsequent mind to expediently eliminate it? “If the mind becomes scattered and distracted, one should gather it in to dwell in right mindfulness”: in the beginning of practice it wanders much, so one gathers it to make it dwell upright. What is right mindfulness that one is told to dwell in it? It is the so-called mind-only, without external perceptual objects. Since delusive objects are absent, mind-only is also tranquil; hence it says, “furthermore, this mind itself also has no self-characteristic, and is unobtainable from thought to thought.”