妙法蓮華經玄義 2.130

2.130

然《勝鬘》說無作四諦中，別取一滅諦，是佛所究竟，是常、是諦、是依，三是無常，非諦，非依。何者？三入有為相中，故無常。無常則虛妄，故非諦。無常則不安，故非依。滅諦離有為，故是常。非虛妄，故是諦。第一安隱，故是依。故名第一義諦，亦名不思議也。

However, the Śrīmālā[-sūtra], in expounding the unconstructed four truths, separately singles out the one truth of cessation as what is fully realized by the Buddha—it is permanent, it is truth, it is a refuge—whereas the other three are impermanent, not truth, and not a refuge. Why so? Because the three fall within conditioned characteristics, they are impermanent. Being impermanent, they are illusory, hence not truth. Being impermanent, they are unstable, hence not a refuge. The truth of cessation is free from the conditioned, hence it is permanent; it is not illusory, hence it is truth; it is supreme peace and security, hence it is a refuge. Therefore it is named the ultimate truth, and also named the inconceivable.