Brihadaranyaka Upanishad 1.5.23

1.5.23

athaiṣa śloko bhavati yataścodeti sūryo'staṃ yatra ca gacchatīti prāṇādvā eṣa udeti prāṇe'stameti taṃ devāścakrire dharmam̐ sa evādya sa u śva iti yadvā ete'murhyadhriyanta tadevāpyadya kurvanti | tasmādekameva vrataṃ caretprāṇyāccaivāpānyācca nenmā pāpmā mṛtyurāpnuvaditi yadyu caretsamāpipayiṣetteno etasyai devatāyai sāyujyam̐ salokatāṃ jayati

Now there is this verse: ‘The gods observed the vow of that from which the sun rises and in which he sets. It is (followed) to-day, and it will be (followed) to-morrow.’ The sun indeed rises from the vital force and also sets in it. What these (gods) observed then, they observe to this day. Therefore a man should observe a single vow—do the functions of the Prāṇa and Apāna (respiration and excretion), lest the evil of death (fatigue) should overtake him. And if he observes it, he should seek to finish it. Through it he

1.5.23.p1

iti prathamādhyāye pañcamaṃ brāhmaṇam