Chandogya Upanishad 4.6

agniṣṭe pādaṃ vakteti sa ha śvo bhūte gā abhiprasthāpayāṃcakāra tā yatrābhisāyaṃ babhūvus tatrāgnim upasamādhāya gā uparudhya samidham ādhāya paścād agneḥ prāṅ upopaviveśa

'Agni will declare to you another foot of Brahman.' (After these words of the bull), Satyakâma, on the morrow, drove the cows (toward the house of the teacher). And when they came towards the evening, he lighted a fire, penned the cows, laid wood on the fire, and sat down behind the fire, looking to the east.

tam agnir abhyuvāda satyakāma 3 iti bhagava iti ha pratiśuśrāva

Then Agni (the fire) said to him: 'Satyakâma!' He replied: 'Sir.'

brahmaṇaḥ somya te pādaṃ bravāṇīti bravītu me bhagavān iti tasmai ha uvāca pṛthivī kalā antarikṣaṃ kalā dyauḥ kalā samudraḥ kalā eṣa vai somya catuṣkalaḥ pādo brahmaṇo 'nantavān nāma

Agni said: 'Friend, I will declare unto you one foot of Brahman.' 'Declare it, Sir,' he replied. He said to him: 'The earth is one quarter, the sky is one quarter, the heaven is one quarter, the ocean is one quarter. This is a foot of Brahman, consisting of four quarters, and called Anantavat (endless).

sa ya etam evaṃ vidvāṃś catuṣkalaṃ pādaṃ brahmaṇo 'nantavān ity upāste 'nantavān asmiṃl loke bhavati anantavato ha lokāñ jayati ya etam evaṃ vidvāṃś catuṣkalaṃ pādaṃ brahmaṇo 'nantavān ity upāste

'He who knows this and meditates on the foot of Brahman, consisting of four quarters, by the name of Anantavat, becomes endless in this world. He conquers the endless worlds, whoever knows this and meditates on the foot of Brahman, consisting of four quarters, by the name of Anantavat.