成唯識論述記 2.21

2.21

述曰：下難無方分，略有五難，此第一極微無方分，應無光影難。無方分者，是薩婆多計，彼以極微等即是和合色，和合色外無別極微，極微外無和合色。以理難云：汝和合色應無方分，體即極微故，如汝極微成和合色，無方分已。遂立量云：汝和合色等不能承光發影，無方分故；如非色等。

The Commentary states: Below, challenging the lack of spatial parts, there are roughly five objections. This first is the objection that if atoms lack spatial parts, there should be no light and shadow. Lacking spatial parts is the tenet of the Sarvāstivāda; they hold that atoms and the like are precisely composite matter, that there are no separate atoms outside composite matter, and no composite matter outside atoms. Challenging through reason: 'Your composite matter should lack spatial parts, because its substance is precisely the atoms, just as your atoms form composite matter and already lack spatial parts.' Hence the formal inference is established: 'Your composite matter and the like cannot catch light and cast a shadow; because they lack spatial parts; like non-material entities and the like.'