Vaisesika Sūtra 8.1.04

गुणकर्मसु संनिकृष्टेषु ज्ञाननिष्पत्तेर्द्रव्यं कारणम् ॥४॥

guṇakarmasu saṃnikṛṣṭeṣu jñānaniṣpatter dravyaṃ kāraṇam ॥4॥

[गुण (guṇa) - quality; कर्मसु (karmasu) - in actions; सन्निकृष्टेषु (saṃnikṛṣṭeṣu) - in those which are in contact; ज्ञान (jñāna) - knowledge; निष्पत्तेः (niṣpatter) - of the arising; द्रव्यं (dravyaṃ) - substance; कारणम् (kāraṇam) - cause;]

The qualities and actions of the substances that are in contact are the cause for the production of knowledge.