Bṛhadāraṇyaka Upaniṣad 6.4.22

Hiranmayi arani yabhyam nirmanthatam asvinau, tam te garbham havamahe dasame masi sutave. Yathagnigarbha prithivi, yatha dyaur indrena garbhini, vayur disam yatha garbha evam garbham dadhami te 'sav iti.