Vaisesika Sūtras
Vaisesika Sūtra 3.1.03
सोऽनपदेशः ॥३॥
so'napadeśaḥ ॥3॥
[सः (saḥ) - that (entity); अनपदेशः (anapadeśaḥ) - not verbally expressible.]
That is not verbally expressible.