成唯識論述記 2.909

2.909

述曰：即復難言：此真如體既許為因，應有取、與，以體前後無轉變故，無取、無與，故不為因。下六義中第一、剎那滅，即簡真如非心因緣，因有生滅，有取、與故。一切無為為所緣緣，此亦無妨；因緣不然，親能辨體與力生故。

The Commentary states: Then he challenges them again: If the substance of this tathatā is admitted to be a cause, it should have apprehension and bestowal; because its substance undergoes no transformation before or after, it lacks apprehension and bestowal, so it cannot be a cause. Among the six characteristics below, the first—destruction in an instant (kṣaṇika)—rules out tathatā from being the cause and condition of mind, for a cause entails production and cessation, having apprehension and bestowal. All unconditioned dharmas can serve as objective conditions (ālambana-pratyaya), which presents no problem; but cause and condition (hetu-pratyaya) is not so, because it must directly accomplish substance and give power to produce.