Vaisesika Sūtra 2.2.29

न चासिद्धं विकारात् ॥२९॥

na cāsiddhaṁ vikārāt ॥29॥

[न (na): Not; च (ca): And; असिद्धं (asiddhaṁ): not proved; विकारात् (vikārāt): From modification or change;]

and, it (the sound produced by the word) is not disproved because of its modifications.