རབ་འབྱོར་ཐེག་པ་དེས་སུ་ཡང་ངེས་པར་འབྱུང་བར་འགྱུར་བ་མེད་དོ། །
If you ask why, Su­bhūti, it is because all those things associated with this vehicle, and with those who would attain emancipation, and that in which emancipation is attained, are non-existent and they are non-apprehensible.
Space, Buddhism, Boundaries