Chandogya Upanishad 2.2

lokeṣu pañcavidhaṃ sāmopāsīta pṛthivī hiṅkāraḥ agniḥ prastāvaḥ antarikṣam udgīthaḥ ādityaḥ pratihāraḥ dyaur nidhanam ityūrdhveṣu

Let a man meditate on the fivefold Sâman as the five worlds. The hinkâra is the earth, the prastâva the fire, the udgîtha the sky, the pratihâra the sun, the nidhana heaven; so in an ascending line.

athāvṛtteṣu dyaur hiṅkāraḥ ādityaḥ prastāvaḥ antarikṣam udgīthaḥ agniḥ pratihāraḥ pṛthivī nidhanam

In a descending line, the hinkâra is heaven, the prastâva the sun, the udgîtha the sky, the pratihâra the fire, the nidhana the earth.

kalpante hāsmai lokā ūrdhvāś cāvṛttaś ca ya etad evaṃ vidvāṃl lokeṣu pañcavidhaṃ sāmopāste

The worlds in an ascending and in a descending line belong to him who knowing this meditates on the fivefold Sâman as the worlds.