Chandogya Upanishad 8.6.5

8.6.5

atha yatraitad asmāc charīrād utkrāmati \
athaitair eva raśmibhir ūrdhvam ākramate \
sa om iti vā hod vā mīyate \
sa yāvat kṣipyen manas tāvad ādityaṃ gacchati \
etad vai khalu lokadvāraṃ viduṣāṃ prapadanaṃ nirodho 'viduṣām \\806.5\

But when he thus departs from this body, then he proceeds upwards through these very rays, (if a knower) he surely goes up meditating on Om or (does not go up if he is not a knower). As long as it takes for the mind to travel, in that (short) time, he goes to the sun. That indeed is the door to the world (of Brahman), an entrance for the knowers and a shutting out for the ignorant.