成唯識論述記 3.729

3.729

述曰：此第四因，即唯約六波羅蜜論。不爾，即與一切行中，修一切行無有差別，以一一行中，皆能修集一切行故。

The Commentary states: This is the fourth cause, which is spoken of only in terms of the six pāramitās. Were it not so, there would be no distinction from cultivating all practices within all practices, because within each single practice they are able to cultivate and amass all practices.