Vaisesika Sūtra 8.1.10

द्रव्येष्वनितरेतकारणाः ॥१०॥

dravyeṣvanitaretakāraṇāḥ ॥10॥

[द्रव्येषु (dravyeṣu) - in substances; अनितर (anitara) - not other; एत (eta) - these; कारणाः (kāraṇāḥ) - causes;]

These causes are present in substances, not elsewhere.