Mandukya Karika, verse 3.43


दुःखं सर्वमनुस्मृत्य कामभोगान्निवर्तयेत् ।
अजं सर्वमनुस्मृत्य जातं नैव तु पश्यति ॥ ४३ ॥

duḥkhaṃ sarvamanusmṛtya kāmabhogānnivartayet |
ajaṃ sarvamanusmṛtya jātaṃ naiva tu paśyati || 43 ||

43. The mind should be turned back from the enjoyment of pleasures, remembering that all this is attended with misery. If it be remembered that everything is the unborn (Brahman), the born (duality) will not be seen.

Shankara Bhashya (commentary)

What is the way of disciplining the mind? It is thus replied: Remember that all1 duality is caused by Avidyā or illusion and therefore afflicted with misery. Thereby dissuade the mind from seeking enjoyments produced by desires. In other words, withdraw the mind from all dual objects by impressing upon it the idea of complete non-attachment.2 Realise from the teachings of the Scriptures and the Āchāryās that all this is verily the changeless Brahman. Then you will not see anything to the contrary, viz., duality; for it does not exist.