Bg 17.17

śraddhayā parayā taptaṁ
tapas tat tri-vidhaṁ naraiḥ
aphalākāṅkṣibhir yuktaiḥ
sāttvikaṁ paricakṣate
śraddhayā — with faith; parayā — transcendental; taptam — executed; tapaḥ — austerity; tat — that; tri-vidham — of three kinds; naraiḥ — by men; aphala-ākāṅkṣibhiḥ — who are without desires for fruits; yuktaiḥ — engaged; sāttvikam — in the mode of goodness; paricakṣate — is called.
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.