Vaisesika Sūtra 5.2.15

आत्मेन्द्रियमनोर्थसंनिकर्षात् सुखदुःखे ॥१५॥

ātmaindriyamanōrthasaṁnikarṣāt sukhaduḥkhē ॥15॥

[आत्म-इन्द्रिय-मनस्-अर्थ-संनिकर्षात् (ātma-indriya-manas-artha-saṁnikarṣāt) - from conjunction of ātman, senses, mind, and object; सुख-दुःखे (sukha-duḥkhe) - pleasure and pain;]

Pleasure and pain arise from the conjunction of the ātman, the senses, the mind, and the object.