Vaisesika Sūtra 4.2.10

संज्ञाया अनादित्वात् ॥१०॥

sañjñāyā anāditvāt ॥10॥

[संज्ञायाः (sañjñāyāḥ) - of designation; अनादित्वात् (anāditvāt) - due to beginninglessness;]

Because designation (of the ātman) is beginningless.