Verse 4.10.4

अथ हाग्नयः समूदिरे तप्तो ब्रह्मचारी कुशलं नः पर्यचारीद्धन्तास्मै प्रब्रवामेति तस्मै होचुः प्राणो ब्रह्म कं ब्रह्म खं ब्रह्मेति ॥ ४.१०.४ ॥

atha hāgnayaḥ samūdire tapto brahmacārī kuśalaṃ naḥ paryacārīddhantāsmai prabravāmeti tasmai hocuḥ prāṇo brahma kaṃ brahma khaṃ brahmeti || 4.10.4 ||

4. Then the fires—the Dakṣiṇāgni, the Gārhapatya, and the Āhavanīya—began to say to each other: ‘This brahmacārin has become thin from practising austerities. He has so long looked after us with great care. Let us teach him.’ They said to Upakosala, ‘Prāṇa is Brahman, ka [happiness] is Brahman, and kha [space] is Brahman.’

Word-for-word explanation:

Atha ha agnayaḥ samūdire, then the fires [the Dakṣiṇāgni, the Gārhapatya, and the Āhavanīya] began to say; taptaḥ brahmacārī, the austere brahmacārin; kuśalam, with great care; naḥ paryacārīt, looked after us; hanta asmai prabravāma iti, so we will teach him; tasmai ha ucuḥ, they said to him; prāṇaḥ brahma, prāṇa is Brahman; kam brahma, happiness is Brahman; kham brahma iti, ākāśa [space] is Brahman.

Commentary:

The three fires that had been so well taken care of by Upakosala were moved to see his condition. They also felt that a great injustice had been done to him by his teacher, Satyakāma. They then decided to take it upon themselves to teach him.