KAṬHA UPANISHAD · 2.1.6

यः पूर्वं तपसो जातमद्भ्यः पूर्वमजायत ।
गुहां प्रविश्य तिष्ठन्तं यो भूतेभिर्व्यपश्यत । एतद्वै तत् ॥ ६॥

yaḥ pūrvaṃ tapaso jātamadbhyaḥ pūrvamajāyata ।
guhāṃ praviśya tiṣṭhantaṃ yo bhūtebhirvyapaśyata । etadvai tat ॥ 6॥

He is the seer that seeth Him who came into being before austerity and was before the waters; deep in the heart of the creature he seeth Him, for there He standeth by the mingling of the elements. This is the thing thou seekest.