Vaisesika Sūtra 10.1.06

एकार्थसमवायिकारणान्तरेषु द्रुष्टत्वात् ॥६॥

ekārtha-samavāyikāraṇa-antareṣu dṛṣṭatvāt ॥6॥

[एकार्थ (ekārtha) - having one purpose; समवायिकारणान्तरेषु (samavāyikāraṇa-antareṣu) - in other inherent causes; दृष्टत्वात् (dṛṣṭatvāt) - due to being observed;]

Because other inherent causes for the same effect have been observed (else where).