俱舍論記 20.37

20.37

「論曰至許常有故」者，釋何礙用。經部難云：應說一切有為諸法於三世中自體恒有，應一切時能起作用，何礙此法用有還無。汝若謂眾緣不和合者，此救非理，汝許因緣亦常有故。

Regarding "The treatise says ... because it is admitted to exist constantly": this explains "what obstructs activity". The Sautrāntika objects, saying: One must say that all conditioned dharmas constantly exist in their intrinsic substance across the three periods of time; they should be able to initiate activity at all times—what obstructs this dharma's activity from existing and then becoming non-existent? If you say that the various conditions are not assembled, this rescue is illogical, because you admit that causes and conditions also exist constantly.