成唯識論述記 5.961

5.961

述曰：彼惡業故，令彼有情五根之中，皆受苦故，所以定成。必令有男、女根，於彼何用？非男、女根處能受苦故。

The Commentary states: It is because of their bad karma that those sentient beings undergo suffering in all five faculties, and therefore they definitely possess them. What use would they have there for definitely being made to possess the male or female faculty? For the site of the male or female faculty cannot undergo suffering there.