成唯識論述記 4.858

4.858

述曰：如《瑜伽》第一等說：六識皆有三依，謂因緣依等。汝之五識依但應二，以種子為但有根故，與因緣根無別體故但應二。

The Commentary states: As stated in Fascicle 1 and elsewhere of the Yogācārabhūmi: the six consciousnesses all have three supports, namely the causal condition support and so forth. Your five consciousnesses should only have two supports, because taking seeds to be the co-arising faculty means it has no separate substance from the causal condition faculty, and therefore there should only be two.