Srimad Bhagavatam Canto 11, Chapter 15, Text 24

SB 11.15.24

parsnyapidya gudam pranam
aropya brahma-randhrena
 brahma nitvotsrjet tanum
The yogi who has achieved the mystic perfection called svacchanda-mrtyu blocks the anus with the heel of the foot and then lifts the soul from the heart to the chest, to the neck and finally to the head. Situated within the brahma-randhra, the yogi then gives up his material body and guides the spirit soul to the selected destination.
This mystic opulence of svacchandu-mrtyu, or dying at will, was wonderfully exhibited by Bhismadeva at the end of the Battle of Kuruksetra. According to Srila Sridhara Svami, the term brahma, as used in this verse, is an example of upalaksana, or the use of a general term to indicate various concepts. Brahma here indicates the particular destination selected by the yogi, namely the spiritual sky, the impersonal brahmajyoti or any other destination that has attracted the yogi’s mind.
Srimad Bhagavatam Canto 11, Chapter 15, Text 23
Srimad Bhagavatam Canto 11, Chapter 15, Text 25