Vaisesika Sūtra 5.1.03

अभिघातजे मुसलादौ कर्मणि व्यतिरेकादकारणं हस्तसंयोगः ॥३॥

abhighātaje musalādau karmaṇi vyatirekād akāraṇaṁ hastasaṁyogaḥ ॥3॥

[अभिघातजे (abhighātaje) - arising from impact; मुसल-आदौ (musala-ādau) - in pestle and the like; कर्मणि (karmaṇi) - in the action; व्यतिरेकात् (vyatirekāt) - due to distinction; अकारणं (akāraṇaṁ) - not a cause; हस्त-संयोगः (hasta-saṁyogaḥ) - conjunction of hand;]

The impact arising from the movement of the pestle and the like, is due to distinct cause and not due to the conjunction of the hand.