BṚHADĀRAṆYAKA UPANISHAD · 1.1.2

अहर् वा अश्वं पुरस्तान् महिमान्वजायत ।
तस्य पूर्वे समुद्रे योनिः ।
रात्रिर् एनं पश्चान् महिमान्वजायत ।
तस्यापरे समुद्रे योनिर् ।
एतौ वा अश्वं महिमानाव् अभितः सम्बभूवतुः ।
हयो भूत्वा देवान् अवहद् वाजी गन्धर्वान् अर्वासुरान् अश्वो मनुष्यान् ।
समुद्र एवास्य बन्धुः समुद्रो योनिः ॥

ahar vā aśvaṃ purastān mahimānvajāyata ।
tasya pūrve samudre yoniḥ ।
rātrir enaṃ paścān mahimānvajāyata ।
tasyāpare samudre yonir ।
etau vā aśvaṃ mahimānāv abhitaḥ sambabhūvatuḥ ।
hayo bhūtvā devān avahad vājī gandharvān arvāsurān aśvo manuṣyān ।
samudra evāsya bandhuḥ samudro yoniḥ ॥

Verily Day arose after the horse as the (golden) vessel, called Mahiman (greatness), which (at the sacrifice) is placed before the horse. Its place is in the Eastern sea. The Night arose after the horse as the (silver) vessel, called Mahiman, which (at the sacrifice) is placed behind the horse. Its place is in the Western sea. Verily, these two vessels (or greatnesses) arose to be on each side of the horse. As a racer he carried the Devas, as a stallion the Gandharvas, as a runner the Asuras, as a horse men. The sea is its kin, the sea is its birthplace.

F. Max Müller · The Upanishads, Sacred Books of the East 15 (1884)