摩訶止觀 5.190

5.190

「云何不生不生不可說？以修道得故。」今解：「修道得」者，乃是極果所證；尚非下十地所知，豈可言說？據此知是界外之解也。

"Why is non-arising non-arising ineffable? Because it is attained through cultivating the path." It is now explained: "attained through cultivating the path" refers to what is realized in the ultimate fruit; it is not even known by those below the tenth stage—how could it be expressed in words? Based on this, we know this is understanding outside the realms.