BṚHADĀRAṆYAKA UPANISHAD · 3.7.13

यस् तमसि तिष्ठंस् तमसो ऽन्तरो यं तमो न वेद यस्य तमः शरीरं यस् तमो ऽन्तरो यमयत्य् एष त आत्मान्तर्याम्य् अमृतः ॥

yas tamasi tiṣṭhaṃs tamaso ’ntaro yaṃ tamo na veda yasya tamaḥ śarīraṃ yas tamo ’ntaro yamayaty eṣa ta ātmāntaryāmy amṛtaḥ ॥

'He who dwells in the darkness (tamas), and within the darkness, whom the darkness does not know, whose body the darkness is, and who pulls (rules) the darkness within, he is thy Self, the puller (ruler) within, the immortal.'