Chāndogya Upaniṣad 6.8.5

6.8.5

atha yatraitat puruṣaḥ pipāsati nāma teja eva tat pītaṃ nayate \
tad yathā gonāyo 'śvanāyaḥ puruṣanāya ity evaṃ tat teja ācaṣṭa udanyeti \
tatraitad eva śuṅgam utpatitaṃ somya vijānīhi \
nedam amūlaṃ bhaviṣyatīti \\608.5\

5. Now, when a person here is thirsty, as it is called, just heat is leading off that which has been drunk. So, as they speak of "a leader-of-cows" (go-nāya), "a leader-of-horses" (aśva-nāya), "a leader-of-men" (puruṣa-nāya), so one speaks of heat as "a leader-of-water" (uda-nyā, thirst).

On this point, my dear, understand that this [body] is a sprout which has sprung up. It will not be without a root.