Mandukya Karika, verse 1.10


निवृत्तेः सर्वदुःखानामीशानः प्रभुरव्ययः ।
अद्वैतः सर्वभावानां देवस्तुर्यो विभुः स्मृतः ॥ १० ॥

nivṛtteḥ sarvaduḥkhānāmīśānaḥ prabhuravyayaḥ |
advaitaḥ sarvabhāvānāṃ devasturyo vibhuḥ smṛtaḥ || 10 ||

10. In it, indicated as the changeless and the Supreme Lord, there is a cessation of all miseries. It is the one without a second among all entities. It is known as the Turīya (Fourth), effulgent and all-pervading.

Shankara Bhashya (commentary)

In (the Knowledge of) Īśāna, meaning the Turīya Ātman there is a cessation1 of all miseries characterised by the three states, viz., Prājña,2 Taijasa and Viśva. The word ‘Īśāna’ is explained as ‘Prahhu’, i.e., the one who brings about the cessation of miseries. It is because misery is destroyed by one’s own Knowledge of it (Turīya). ‘Avyaya’ means that which is not subject to any change, i.e., which does not deviate from its own nature. How? It is so because Turīya is non-dual, all4 other entities being illusory (unreal) like the idea of the snake, etc., imagined in the rope. It is he who is recognised5 as the Deva (on account of his effulgent nature), the Turīya, the fourth, the Vibhu,6 that is the all-pervading one.