The Bhagavad Gita by Eknath Easwaran

The Eternal Godhead ╯
through the brahmarandhra, there will be no rebirth: that
is, the dying person will enter samadhi at the time of death.
In samadhi, prana is withdrawn from lower levels of awareness
to rush upwards to the seventh center at the crown of the
head. This is possible only for the yogi who has thoroughly
mastered meditation and the control of prana. If prana exits
through some other one of the eleven doors of the body, the
Upanishads say, the state of immortality will not be gained:
When he departs from this body, he ascends with the rays
of the sun, repeating the syllable Om . As soon as he thinks
of it, he comes to the sun. That, indeed, is the door to the
next world. Those who know enter; those who do not know
are stopped. There is a verse:
A hundred and one subtle tracks lead from the heart;
One of these goes upwards to the crown of the head.
Going up by it, he goes to eternal life.
Others depart in various directions.
(Chandogya Upanishad viii.6.5–6)
In the Gita, as well as in this passage from the Chandogya
Upanishad, the mantram Om is used. If the yogis can remember
the mantram even as consciousness itself is departing the
body – and, the Gita adds, if they can meditate on Krishna
– they will go to the “highest goal.” Relinquishing the body in
a state of samadhi, they attain the mystic eternity that is union
with Krishna.
161 ╯