Vaisesika Sūtra 7.1.05

अनित्येष्वनित्या द्रव्यानित्यत्वात् ॥५॥

anityeṣv-anityā dravya-anityatvāt ॥5॥

[अनित्येषु (anityeṣu) - in impermanent; अनित्याः (anityāḥ) - impermanent; द्रव्य (dravya) - substance; अनित्यत्वात् (anityatvāt) - due to impermanence;]

In impermanent things, they are impermanent due to the impermanence of the substance.