One verse

Bhagavad Gita 17.17

17.17

श्रद्धया परया तप्तं तपस्तत्त्रिविधं नरैः | अफलाकाङ्क्षिभिर्युक्तैः सात्त्विकं परिचक्षते ||१७-१७||

śraddhayā parayā taptaṃ tapastattrividhaṃ naraiḥ . aphalākāṅkṣibhiryuktaiḥ sāttvikaṃ paricakṣate ||17-17||

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.