CHĀNDOGYA UPANISHAD · 6.15.2

अथ यदास्य वाङ् मनसि संपद्यते मनः प्राणे प्राणस् तेजसि तेजः परस्यां देवतायाम् अथ न जानाति ॥

atha yadāsya vāṅ manasi saṃpadyate manaḥ prāṇe prāṇas tejasi tejaḥ parasyāṃ devatāyām atha na jānāti ॥

'But when his speech is merged in his mind, his mind in breath, breath in heat (fire), heat in the Highest Being, then he knows them not.

F. Max Müller · The Upanishads, Sacred Books of the East 1 (1879)