Vaisesika Sūtra 1.2.15

कर्मसु भावात् कर्मत्वमुक्तम् ॥१५॥

karmasu bhāvāt karmatvamuktam ॥15॥

[कर्मसु भावात् कर्मत्वम् उक्तम्॥
karmasu = in actions; bhāvāt = among the existent; karmatvam = action-ness; uktam = declared as;॥]

The action among the existent is declared as the action-ness.