法華論疏 3.281

3.281

眾生界本來四絕，即涅槃界也。不離眾生界有如來藏故者，上標即，今以不離釋上即也。

The realm of sentient beings is originally severed from the four extremes; it is itself the realm of nirvāṇa. "Because there is no tathāgatagarbha apart from the realm of sentient beings": above, it posited identity; here, it explains the identity above in terms of non-separation.