摩訶止觀 6.147

6.147

上來諸教皆有三位，若定判者，應取下根以明其位。則有二義：一、依教故，二、決不退轉。入假行成，中、上乍有進退，故不約其論位。

In the teachings discussed above, all have three levels of stages. If one is to establish them definitively, one should take the inferior capacity to clarify the stages. This has two meanings: first, because it accords with the teaching; second, because there is definitely no regression. When the practice of entering the provisional is accomplished, the middling and superior capacities may temporarily advance or retreat; therefore, the stages are not defined in terms of them.