As mentioned in Brihadaranyaka upanishad ( बृहदारण्यकोपनिषद् 2.5.18)
स वा अयं पुरूषः सर्वासु पूर्षु पुरिशयो नैनेन किञ्चनानावृतं नैनेन किञ्चनासंवृतम् ।।
Explanation –
पुरिशेत इति पुरिशयः सन् पुरूष इत्युच्यते
Because this Atman resides in this पुर् ( physical body ) , so it is called पुरूषः
This is nothing which is not covered by this पुरूषः ( Atman) and there is nothing in which this पुरूषः ( Atman ) doesn’t resides.
