仁王護國般若波羅蜜多經疏 2.119

2.119

解曰：所言際者，是際畔義，謂有為法墮三世故。三世有二：流轉三世，已往稱前，如前日等；未至稱後，如後日等。法行三世，未至稱前，如言前路；已往稱後，如言過後。色心之法相自遷流，遂成三世。無為實相無前後中，故云無際。從此第二三際即離。

Explanation: What is called a "limit" has the meaning of an extremity or boundary, referring to conditioned dharmas falling into the three periods of time. The three periods of time are of two kinds: In the three periods of saṃsāric transmigration, what has passed is called prior, like the previous day, etc.; what has not yet arrived is called posterior, like the subsequent day, etc. In the three periods of the progression of dharmas, what has not yet arrived is called prior, as in speaking of the road ahead; what has passed is called posterior, as in speaking of what has gone by. Dharmas of form and mind by their own characteristics shift and flow, thereby constituting the three periods of time. The unconditioned real mark has no prior, posterior, or intermediate, and is therefore said to be "without limits". From here is the second, identity and separation regarding the three periods.