Kauṣītaki Upaniṣad 4.20.11

4.20.11

tam etam ātmānam eta ātmāno 'nvavasyante yathā śreṣṭhinaṃ svāḥ /

This selfsame breathing spirit (prāṇa), even the intelligential self (prajñātman), has entered this bodily self (śarīra·ātman) up to the hair and finger-nail tips. (20) Just as a razor might be hidden in a razor-case, or fire in a fire-receptacle, even thus this intelligential self has entered this bodily self up to the hair and the finger-nail tips. Upon that self these selves depend, as upon a chief his own [men]. Just as a chief enjoys his own [men], or as his own [men] are of service to a chief, even thus this intelligential self enjoys these selves ; even thus these selves are of service to that self.