俱舍論疏 6.186

6.186

論「於生不障至道何所作」，答也。六因中能作因，於生不障，名能作因。無為不生，故無能作因也。

On the Śāstra's: "Not obstructing arising [...] what could the path do?": this is the answer. Among the six causes, the efficient cause is named an efficient cause because it does not obstruct arising. The unconditioned does not arise, hence it has no efficient cause.