Bhagavad Gita 17.17
श्रद्धया परया तप्तं तपस्तत्त्रिविधं नरैः। अफलाकाङ्क्षिभिर्युक्तैः सात्त्विकं परिचक्षते।।17.17।।
śraddhayā parayā taptaṃ tapastattrividhaṃ naraiḥ| aphalākāṅkṣibhiryuktaiḥ sāttvikaṃ paricakṣate||17.17||
shraddhaya paraya taptam tapastattrividham naraih aphalakankshibhiryuktaih sattvikam paricakshate17.17
Meaning
This threefold austerity, practiced with utmost faith by people who are not desirous of fruit and who are steadfast and disciplined, is said to be sattvic.
जो त्रिविध तप, परम श्रद्धा से, फल की इच्छा छोड़े हुए, एकाग्रचित्त पुरुषों द्वारा किया जाता है, वही सात्त्विक तप कहा जाता है।
This is verse 17 of 28 in Chapter 17 (Shraddhatraya Vibhaga Yoga) of the Bhagavad Gita.