Bhagavad Gītā Chapter Four verse 28

dravyayajñās tapoyajñā yogayajñās tathāpare |
svādhyāyajñānayajñāśca yatayaḥ saṃśitavratāḥ ||

dravya - a substance, thing, object;the ingredients or materials of anything; medicinal substance or drugyajña - act of worship or devotion; offering, oblation, sacrificetapas - to heat; religious austerity; self-discipline; pain, sufferingyoga - the act of yokingsvādhyāya - to study; to read; sacred recitation; study of the selfjñāna - knowing; knowledge; higher knowledgevrata - vow

Commentaries and Reflections

T Krishnamacharya:

Tapas is an offering for something else, not a deprivation.”