法華文句記 9.189

9.189

應身四中，非報身故非常，非生死故非無常。「兩存」者，雙具前兩。

Within the four of the nirmāṇakāya: not being the saṃbhogakāya, it is not permanent; not being saṃsāra, it is not impermanent. "Both preserved" means fully possessing both of the preceding.