成唯識論述記 4.241

4.241

以下第三破上座部，無性第三云：「經部師」者，即此上座部中自有以經為量者，故言經部。

Below, the third is the refutation of the Sthaviras. Asvabhāva says in the third [section], 'the Sautrāntika masters'—namely, among these Sthaviras themselves there are those who take the sūtras as their authoritative measure (pramāṇa), and hence they are called Sautrāntikas.