KAṬHA UPANISHAD · 2.1.8

अरण्योर्निहितो जातवेदा गर्भ इव सुभृतो गर्भिणीभिः ।
दिवे दिवे ईड्यो जागृवद्भिर्हविष्मद्भिर्मनुष्येभिरग्निः । एतद्वै तत् ॥ ८॥

araṇyornihito jātavedā garbha iva subhṛto garbhiṇībhiḥ ।
dive dive īḍyo jāgṛvadbhirhaviṣmadbhirmanuṣyebhiragniḥ । etadvai tat ॥ 8॥

As a woman carrieth with care the unborn child in her womb, so is the Master of knowledge lodged in the tinders, and day by day should men worship him who live their waking life and stand before him with sacrifice; for he is that Agni. This is the thing thou seekest.

Sri Aurobindo · CWSA 18, p. 118