俱舍論記 5.184

5.184

「且應思擇至有用無用」者，此下經部廣破。此即勸思，未來法體為有、為無，然後可論有用、無用。體尚未定，何須說用？

Regarding "One should first deliberate ... having operation or lacking operation": Below this, the Sautrāntika refutes [them] extensively. This prompts deliberation on whether the substance of future phenomena exists or does not exist; only thereafter may one discuss having operation or lacking operation. When the substance is not yet established, why speak of operation?