首楞嚴義疏注經 4.484

4.484

前佛所勸，意明如來藏體清淨本然，由乎強覺分成六妄。若能返照，從一根門入一性海，法界一相，更無六一之異，故云深入一門六根清淨。今阿難將謂六根有實，元是一體，若是一體又何分六？故今請示一六之由耳。

What the Buddha previously urged was intended to make clear that the substance of the tathāgatagarbha is fundamentally pure in itself, yet due to forced awareness it divides into six falsities. If one can reflect back, entering through a single faculty door into the one ocean of nature, then the dharmadhātu has a single characteristic, with no difference between six and one. Hence he said: 'enter deeply through a single door and the six faculties will become pure.' Now Ānanda supposes that the six faculties exist as real entities and are originally of one substance; but if they are of one substance, why would they divide into six? Therefore he now requests to be shown the cause of the 'one' and the 'six.'