यो मनसि तिष्ठन्मनसोऽन्तरो यं मनो न वेद यस्य मनः शरीरं यो मनोऽन्तरो यमयत्येष त आत्मान्तर्याम्यमृतः ॥३,७.२० ॥
In plain words
He who dwells in the mind, yet is within the mind, whom the mind does not know, whose body the mind is, who from within controls the mind — he is thy Self, the inner controller, the immortal.