Who is Ascetic (तपस्वी) - The Bhagavad Gita
॥ श्रीमद्भगवद्गीता ॥ ॥ ॐ श्री परमात्मने नमः ॥ ॥ अथ श्रीमद्भगवद्गीता ॥
Shree Krishna has explained about different kinds of sacrifices in chapter 4 of Shrimad Bhagavad Gita (mentioned as chapter. verse in this article in bracket). Sacrifices are done by yogis while performing the fire rituals, the duties, the psychic control or dhayan or worship of God.
Different persons perform different kind of sacrifices. Some perform sacrifice with material possessions; some offer sacrifice in the shape of austerities; others sacrifice through the practice of Yoga; while some striving souls, observing austere vows, perform sacrifice in the shape of wisdom through the study of sacred texts (4.28).
Many such forms of sacrifice have been explained in detail in the Vedas. All of them involve the action of mind, senses and body. Thus, knowing the truth about them one shall be freed from the bondage of action (through their performance) (4.32).
Yogis who enjoy the nectar that has been left over after the performance of a sacrifice attain the eternal Brahman. The person, who does not offer sacrifice, is neither happy in this world nor next. Sacrifice through Knowledge, is superior to sacrifice performed with material things. For all actions without exception culminate in Knowledge (4.33).
Sacrifices during Fire Ritual:
Brahman is seen everywhere as a form of sacrifice. Brahman is the ladle (with which oblation is poured into the fire, etc.); Brahman, is the oblation; Brahman is the fire, Brahman itself is the performer of sacrifice and so Brahman itself constitutes the act of pouring the oblation into the fire. And, finally, Brahman is the goal to be reached by him who is absorbed in Brahman as the act of such sacrifice (4.24).
Sacrifices during worship of God:
Some Yogis duly offer sacrifice only in the form of worship to gods, while others perform sacrifice by offering the self by the Self itself in the fire of Brahman i.e. attain oneness with Brahman (4.25).
Sacrifices during performance of duties:
Some sacrifice their senses of perception, into the fires of self-discipline. Other Yogis without attachment & aversions sacrifice the objects of perception into the fires of the senses (4.26).
Sacrifices during Psychic control: