Bhagavad Gita Chapter 17.17
śraddhayā parayā taptaḿ
tapas tat tri-vidhaḿ naraiḥ
aphalākāńkṣibhir yuktaiḥ
sāttvikaḿ paricakṣate
Translation This threefold austerity, performed with transcendental faith by men not expecting material benefits but engaged only for the sake of the Supreme, is called austerity in goodness.