Srimad Bhagavatam Canto 02, Chapter 02, Text 19

SB 2.2.19

ittham munis tuparamed vyavasthito
sva-parsninapidya gudam tato ’nilam
sthanesu satsunnamayej jita-klamah
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
By the strength of scientific knowledge, one should be well situated in absolute realization and thus be able to extinguish all material desires. One should then give up the material body by blocking the air hole [through which stool is evacuated] with the heel of one’s foot and by lifting the life air from one place to another in the six primary places.
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
There are many duratmas who claim to have realized themselves as Brahman and yet are unable to conquer material desires. In the Bhagavad-gita (18.54) it is clearly explained that an absolutely self-realized soul becomes completely aloof from all material desires. Material desires are based on the false ego of the living being and are exhibited by his childish and useless activities to conquer the laws of material nature and by his desire to lord it over the resources of the five elements. With such a mentality, one is led to believe in the strength of material science, with its discovery of atomic energy and space travel by mechanical vehicles, and by such tiny advancements in material science the false egoist tries to challenge even the strength of the Supreme Lord, who can finish all man’s tiny endeavors in less than a second. The well-situated self, or Brahman-realized soul, perfectly understands that the Supreme Brahman, or the Personality of Godhead, is the all-powerful Vasudeva and that he (the self-realized living being) is a part and parcel of the supreme whole. As such, his constitutional position is to cooperate with Him in all respects in the transcendental relation of the served and the servitor. Such a self-realized soul ceases to exhibit his useless activities of attempting to lord it over material nature. Being scientifically well informed, he fully engages himself in faithful devotion to the Lord.
The expert yogi who has thoroughly practiced the control of the life air by the prescribed method of the yoga system is advised to quit the body as follows. He should plug up the evacuating hole with the heel of the foot and then progressively move the life air on and on to six places: the navel, abdomen, heart, chest, palate, eyebrows and cerebral pit. Controlling the life air by the prescribed yogic process is mechanical, and the practice is more or less a physical endeavor for spiritual perfection. In olden days such practice was very common for the transcendentalist, for the mode of life and character in those days were favorable. But in modern days, when the influence of Kali Age is so disturbing, practically everyone is untrained in this art of bodily exercise. Concentration of the mind is more easily attained in these days by the chanting of the holy name of the Lord. The results are more effective than those derived from the inner exercise of the life air.
Srimad Bhagavatam Canto 02, Chapter 02, Text 18
Srimad Bhagavatam Canto 02, Chapter 02, Text 20