यस्त्वचि तिष्ठंस्त्वचोऽन्तरो यं त्वङ्न वेद यस्य त्वक्शरीरं यस्त्वचमन्तरो यमयत्येष त आत्मान्तर्याम्यमृतः ॥३,७.२१ ॥
In plain words
He who dwells in the skin, yet is within the skin, whom the skin does not know, whose body the skin is, who from within controls the skin — he is thy Self, the inner controller, the immortal.