妙法蓮華經玄義 2.131

2.131

達摩欝多羅難此義：然經說佛菩提道，三義故常。一、惑盡故常；二、不從煩惱生故常；三、解滿故常，如眾流歸海。那云道諦無常？

Dharmottara challenged this meaning: Yet the sūtra states that the Buddha's path of bodhi is permanent due to three meanings: first, it is permanent because delusions are exhausted; second, it is permanent because it does not arise from afflictions; third, it is permanent because understanding is complete, like the many streams returning to the sea. Why say that the truth of the path is impermanent?