Vaiśeṣika Sūtra 2.2.25

2.2.25

tasmin dravyaṃ karma guṇa iti saṃśayaḥ |

Sound having thus appeared as an object which contains properties, its being the mark or Ether depends solely on its being an Attribute, Therefore to establish its Attribute-ness, he brings out the trilateral Doubt, and says:

“Doubt arises in respect of sound,”—is the complement of the aphorism. Sound-ness and perceptibility by the ear are observed in Sound. And this gives rise to Doubt whether Sound be an Attribute, or a Substance, or an Action, because the ‘particular,’ i.e., difference or divergence is observed both in homogeneous objects, namely the twenty-three Attributes, and in heterogeneous objects, namely Substances, and Actions. But Doubt, whether it be a Genus, or a Species, or a Combination, does not arise, inasmuch as difference in point of being existent, being produced by a cause, etc., is observed.