Bṛhadāraṇyaka Upaniṣad ("Great Forest Teaching") 2.5.3

2.5.3

ayamagniḥsarveṣāṃ bhūtānāṃ madhvasyāgneḥ sarvāṇi bhūtāni madhu yaścāyamasminnagnai tejomayo'mṛtamayaḥ puruṣo yaścāyamadhyātmaṃ vāṅmayastejomayo'mṛtamayaḥ puruṣo'yamevasa yo'yamātmedamamṛtamidaṃ brahmedam̐ sarvam

This fire is the honey of all beings, and all beings are the honey of this fire. Likewise this bright, immortal person in this fire, and that bright, immortal person, existing as speech in the body (both are madhu). He indeed is the same as that Self, that Immortal, that Brahman, that All.