Vaisesika Sūtra 2.1.21

तदलिङ्गमेक द्रव्यत्वात् कर्मणः ॥२१॥

tadaliṅgameka dravyatvāt karmaṇaḥ ॥21॥

[तत् अलिङ्गम् एक द्रव्यत्वात् कर्मणः॥
tat = that; aliṅgam = without distinguishing mark; eka = alone; dravyatvāt = because of substance-ness;karmaṇaḥ = of action;]

Substance-ness or action alone do not distinguish it.