成唯識論演祕 2.1020

2.1020

舊新俱有，以舊類新，舊亦因緣；汝唯本有，無可為類，故非因緣。

Both old and new exist; by assimilating the old to the new, the old is also a causal condition. In your view of innate seeds alone, there is nothing to assimilate them to, so they are not causal conditions.