Aitareya Upanishad 1.3.11

1.3.11

sa īkṣata kathaṃ nv idaṃ mad ṛte syād iti.
sa īkṣata katareṇa prapadyā iti.
sa īkṣata yadi vācābhivyāhṛtaṃ yadi prāṇenābhiprāṇitaṃ yadi cakṣuṣā dṛṣṭaṃ yadi śrotreṇa śrutaṃ yadi tvacā spṛṣṭaṃ yadi manasā dhyātaṃ yady apānenābhyapānitaṃ yadi śiśnena visṛṣṭam atha ko 'ham iti.

He thought, "How indeed can it be there without Me?" He thought, "Through which of the two ways should I enter?" He thought, "If utterance is done by the organ of speech, smelling by the sense of smell, seeing by the eye, hearing by the ear, feeling by the sense of touch, thinking by the mind, the act of drawing in (or pressing down) by Apāna, ejecting by the procreative organ, then who (or what) am I ?"