Vaisesika Sūtra 3.1.15

अप्रसिद्धोऽनपदेशः॥१५॥

aprasiddho'napadeśaḥ ॥15॥

[अप्रसिद्धः (aprasiddhaḥ) - not commonly known; अनपदेशः (anapadeśaḥ) - not verbally expressible.]

What is not commonly known is not verbally expressible.