俱舍論記 6.172

6.172

「豈不先問至開顯自性」者，經部復責。二名互答，自性難知，故應別門開顯自性。

Regarding 'Was it not asked earlier […] reveal its intrinsic nature?': the Sautrāntikas reproach them again. Answering two names with each other leaves the intrinsic nature difficult to know; therefore, its intrinsic nature should be revealed under a distinct heading.