Verse
द्रव्ययज्ञास्तपोयज्ञा योगयज्ञास्तथापरे ।स्वाध्यायज्ञानयज्ञाश्च यतयः संशितव्रताः ॥
The offering of the striver after perfection may be material and physical (dravyayajña, like that consecrated in worship by the devotee to his deity), or it may be the austerity of self-discipline and energy of his soul directed to some high aim, tapo-yajña, or it may be some form of Yoga (like the prāṇāyāma of the Rajayogins and Hatha-yogins, or any other yoga yajña); or it may be the offerings of reading and knowledge.
Gītā 4·28