One should control all the senses and concentrate the mind within the heart, fixing the life-airs between the eyebrows and fully absorbing oneself in yoga.
Bhagavad Gita - Chapter 8 - Taraka Brahma Yoga - The Yoga of the Supreme
Thus, by chanting the great monosyllable om and remembering Me, when one leaves the material body, he will attain the Supreme Abode.
O Partha, that yogi who is without deviation and constantly remembers Me alone, easily attains Me for he is always connected to Me.
Those great personalities who have attained Me never take birth again in this temporary world of misery, for they have reached the highest destination.
O Arjuna, all planets up to the abode of Brahma are places of birth and rebirth, but those who reach Me never take birth again.
A day of Brahma consists of one thousand yugas and his night also lasts for the same period.
At the beginning of Brahma’s day, all things become manifest from the unmanifest state. When Brahma’s night begins, again they all become unmanifest.
O Partha, all living beings repeatedly take birth again and again. When Brahma’s night approaches they are absorbed into Me once more and with the arrival of Brahma’s day they are born again.
However, beyond this state is another unmanifest state that is eternal and cannot be destroyed when all other beings are annihilated.
It is said to be unmanifest and eternal and is declared to be the ultimate destination, upon attaining which, one never returns. This is My Supreme Abode.