Vaisesika Sūtra 2.2.26

सतोलिङ्गाभावात् ॥२६॥

sato liṅgābhāvāt ॥26॥

[सतः (sataḥ): Of the existent or real; लिङ्ग (liṅga): Distinguishing mark or characteristic; अभाव (abhāva): Absence; आत् (āt): From or due to;]

Because of the absence of distinguishing marks of the existent (in the sound produced by the word).