Maitri (Maitrāyaṇīya) Upaniṣad 2.8

2.8

athopāṃśurantaryāmyamibhavatyantaryāmamupāṃśumetayorantarāle cauṣṇyaṃ māsavadauṣṇyaṃ sa puruṣo'tha yaḥ puruṣaḥ so'gnirvaiśvānaro'pyanyatrāpyuktamayamagnirvaiśvānaro yo'yamanantaḥ puruṣo yenedamannaṃ pacyate yadidamadyate tasyaiṣa ghoṣo bhavati yadetatkarṇāvapidhāya śṛṇoti sa yadotkramiṣyanbhavati nainaṃ ghoṣaṃ śṛṇoti ||

[c] Now, the Upāṁśu vessel is over against the Antaryāma vessel, and the Antaryāma vessel over against the Upāṁśu vessel. Between these two, God (_deva_) generated heat. The heat is a person, and a person is the universal fire (Agni Vaiśvānara). It has elsewhere been said: 'This is the universal fire, namely that which is here within a person, by means of which the food that is eaten is cooked. It is the noise thereof that one hears on covering the ears thus. When he [i. e. a person] is about to depart, one hears not this sound.'