首楞嚴義疏注經 10.168

10.168

由定所攝，無行陰使，雖存六根，識不馳散，故云虛靜無復馳逸。唯專內境，定心內照，故云內內湛明。又內內者，深深寂照也，窮到識陰，更無所見，名入無所入。

Gathered in by samādhi and without the instigation of the aggregate of formations, although the six sense faculties remain, consciousness does not gallop or scatter; hence it is said that "they are empty and quiet, no longer galloping outward". Focusing solely on the internal realm, the mind in samādhi internally illuminates; hence it is said that "within the interior it is clear and luminous". Furthermore, "within the interior" means deeply and profoundly tranquil and illuminating; reaching the bottom of the aggregate of consciousness, there is nothing further to be seen, which is called "entering where there is nothing to enter".