Bhagavad Gita 17.17

श्रद्धया परया तप्तं तपस्तत्ित्रविधं नरैः।अफलाकाङ्क्षिभिर्युक्तैः सात्त्विकं परिचक्षते॥

śraddhayā parayā taptaṃ tapastatिtravidhaṃ naraiḥ |aphalākāṅkṣibhiryuktaiḥ sāttvikaṃ paricakṣate ||

This threefold austerity, practiced by steadfast men, with the utmost faith, desiring no reward, is called Sattvic.

These threefold austerities, performed with faith and without thought of reward, can truly be considered pure.

Our plain-language meaning of this verse is waiting for scholar review.