Vaisesika Sūtra 2.2.24

नापि कर्माचाक्षुषत्वात् ॥२४॥

nāpi karmācākṣuṣatvāt ॥24॥

[न (na): Not; अपि (api): Also; कर्म (karma): Action; अच (aca): Not; अक्षुषत्व (akṣuṣatva): Being the object of the eyes or perception; आत् (āt): From;]

Also, (sound of the word) is not action, as it is not the object of perception.