成唯識論述記 6.100

6.100

述曰：其相見道為十六心，觀境應無等持，以要前後唯緣一境故。彼一一念皆住其心，於一境轉，深取所緣，故有定也。

The Commentary states: In the conditioned path of seeing (ākāra-darśanamārga), which consists of sixteen minds observing objects, there would have to be no samādhi, because [under their view] earlier and later moments would necessarily have to cognize only a single object. Since each and every thought-moment has its mind abiding and operating on one object, deeply grasping the intentional object, concentration is present.