因明入正理論疏 2.170

2.170

述曰：第五，俱分有二，此初標名舉宗、因。聲、勝二論皆說聲無質礙，無質礙故，空大為耳根亦無質礙。今聲論對勝論立聲常宗，無質礙因。

Commentary: Fifth, [the reason that occurs in] a part of both classes has two sections; this first sets forth the name and presents the thesis and the reason. Both the Śabdavāda and the Vaiśeṣika treatises state that sound lacks tangible obstruction; because it lacks tangible obstruction, the space element as the auditory organ also lacks tangible obstruction. Now the Śabdavādin establishes against the Vaiśeṣika the thesis that sound is permanent, with the reason "because it lacks tangible obstruction."