Vaisesika Sūtra 3.1.16

आसन् सन्संदिग्धश्चाऽनपदेशः ॥१६॥

āsan san saṁdigdhaś cā'napadeśaḥ ॥16॥

[आसन् (āsan) - having existed; सन् (san) - being; संदिग्धः (saṁdigdhaḥ) - uncertain or doubtful; च (ca) - and; अनपदेशः (anapadeśaḥ) - not verbally expressible.]

That which has existed, yet being uncertain, is not verbally expressible.