Chandogya Upanishad
sa yad aśiśiṣati yat pipāsati yan na ramate tā asya dīkṣāḥ
When a man (who is the sacrificer) hungers, thirsts, and abstains from pleasures, that is the Dikshâ (initiatory rite).
atha yad aśnāti yat pibati yad ramate tad upasadair eti
When a man eats, drinks, and enjoys pleasures, he does it with the Upasadas (the sacrificial days on which the sacrificer is allowed to partake of food).
atha yaddhasati yaj jakṣati yan maithunaṃ carati stutaśastrair eva tad eti
When a man laughs, eats, and delights himself, he does it with the Stuta-sastras (hymns sung and recited at the sacrifices).
atha yat tapo dānam ārjavam ahiṃsā satyavacanam iti tā asya dakṣiṇāḥ
Penance, liberality, righteousness, kindness, truthfulness, these form his Dakshinâs (gifts bestowed on priests, &c.)
tasmād āhuḥ soṣyaty asoṣṭeti punar utpādanam evāsya tat maraṇam evāvabhṛthaḥ
Therefore when they say, 'There will be a birth,' and 'there has been a birth' (words used at the Soma-sacrifice, and really meaning, 'He will pour out the Soma-juice,' and 'he has poured out the Soma-juice'), that is his new birth. His death is the Avabhritha ceremony (when the sacrificial vessels are carried away to be cleansed).
taddhaitad ghora āṅgirasaḥ kṛṣṇāya devakīputrāyoktvovāca apipāsa eva sa babhūva so 'ntavelāyām etat trayaṃ pratipadyetākṣitam asy acyutam asi prāṇasaṃśitam asīti tatraite dve ṛcau bhavataḥ
Ghora Ângirasa, after having communicated this (view of the sacrifice) to Krishna, the son of Devaki— and he never thirsted again (after other knowledge)— said: "Let a man, when his end approaches, take refuge with this Triad:'Thou art the imperishable;' 'Thou art the unchangeable,' 'Thou art the edge of Prâna.' On this subject there are two Rik verses (Rig-veda VIII, 6, 30):—
ādit pratnasya retasaḥ ud vayaṃ tamasaspari jyotiḥ paśyanta uttaram svaḥ paśyanta uttaram devaṃ devatrā sūryam aganma jyotir uttamam iti jyotir uttamam iti
'Then they see (within themselves) the everpresent light of the old seed (of the world, the Sat), the highest, which is lighted in the brilliant (Brahman)." Rig-veda I, 50, 10:— 'Perceiving above the darkness (of ignorance) the higher light (in the sun), as the higher light within the heart, the bright source (of light and life) among the gods, we have reached the highest light, yea, the highest light.'