Mandukya Karika, verse 4.75


अभूताभिनिवेशोऽस्ति द्वयं तत्र न विद्यते ।
द्वयाभावं स बुद्ध्वैव निर्निमित्तो न जायते ॥ ७५ ॥

abhūtābhiniveśo'sti dvayaṃ tatra na vidyate |
dvayābhāvaṃ sa buddhvaiva nirnimitto na jāyate || 75 ||

75. Man has mere persistent belief in the reality of the unreal (which is duality). There is no duality (corresponding to such belief). One who has realised the absence of duality is never born again as there remains, no longer, any cause (for such birth).

Shankara Bhashya (commentary)

As objects are, really speaking, non-existent, therefore people who believe in their existence have, in fact, attachment for duality which is unreal. It is a mere belief in the (existence of) objects which (really speaking) do not exist. There is no duality. The cause of birth is this attachment. Therefore one who has realised the unreality of duality is never born again as he is free from the cause (of birth), viz., attachment to the illusory duality.