Brihadaranyaka Upanishad 6.1.12

6.1.12

reto hoccakrāma tatsaṃvatsaraṃ proṣyāgatyovāca kathamaśakata madṛte jīvitumiti te hocuryathā klībā aprajāyamānā retasā prāṇantaḥ prāṇenavadanto vācā paśyantaścakṣuṣā śṛṇvantaḥ śrotreṇa vidvām̐so manasaivamajīviṣmeti praviveśa ha retaḥ

The organ of generation went out. After staying a whole year out it came back and said, ‘How did you manage to live without me?’ They said, ‘We lived just as eunuchs do, without having children through the organ of generation, but living through the vital force, speaking through the organ of speech, seeing through the eye, hearing through the ear and knowing through the mind.’ So the organ of generation entered.