俱舍論頌疏論本 1.204

1.204

有情生所依者，明無漏識非識界所以也，由許六界是諸有情生所依故。若無漏法破壞三有，非生所依故，無漏識非識界也。

'The support for the birth of sentient beings' clarifies the reason why undefiled consciousness is not the consciousness element: it is because the six elements are accepted as the supports for the birth of all sentient beings. Undefiled phenomena destroy the three realms of existence and are not supports for birth; therefore, undefiled consciousness is not the consciousness element.