Mandukya Karika, verse 4.80

Text

निवृत्तस्याप्रवृत्तस्य निश्चला हि तथा स्थितिः ।
विषयः स हि बुद्धानां तत्साम्यमजमद्वयम् ॥ ८० ॥

nivṛttasyāpravṛttasya niścalā hi tathā sthitiḥ |
viṣayaḥ sa hi buddhānāṃ tatsāmyamajamadvayam || 80 ||

80. The mind, thus freed from attachment (to all external objects) and undistracted (by fresh objects) attains to its state of Immutability. Being actually realised by the wise, it is undifferentiated, birthlcss and non-dual.

Shankara Bhashya (commentary)

When the mind is withdrawn from all duality of objects, and when it does not attach itself to any objects,—as no objects exist—then the mind attains to the state of immutability which1 is of the same nature as Brahman. This2 realisation of the mind as Brahman is characterised by the mass of unique non-dual consciousness. As that condition of the mind is3 known,, (only) by the wise who have known the Ultimate Reality, that state is supreme and undifferentiated, birthless and non-dual.