Maitri (Maitrāyaṇīya) Upaniṣad 6.2

6.2

atha ya eṣo'ntare hṛtpuṣkara evāśrito'nnamatti sa eṣo'gnirdivi śritaḥ sauraḥ kālākhyo'dṛśyaḥ sarvabhūtānyannamattīti kaḥ puṣkaraḥ kiṃmayo veti iadaṃ vā va tatpuṣkaraṃ yo'yamākāśo'syemāḥ catasro diśaścatasra upadiśo dalasaṃsthā āsamarvāgvicarata etau prāṇādityā etā upāsitomityetadakṣareṇa vyāhṛtibhiḥ sāvitryā ceti ||

2. Now, He who dwells within the lotus of the heart and eats food, is the same as that solar fire which dwells in the sky, called Time, the invisible, which eats all things as his food.

What is the lotus, and of what does it consist?

This lotus, assuredly, is the same as space. These four quarters of heaven and the four intermediate quarters are the form of its leaves.

These two, the breathing spirit and the sun, go forth toward each other.

One should reverence them with the syllable _Om_ [§ 3-5], with the Mystic Utterances (_vyāhṛti_) [§ 6], and with the Sāvitrī Prayer [§ 7].