Tripura Rahasya

Tripura Rahasya is an ancient prime text on Advaita in Sanskrit and was highly commended by Bhagavan Sri Ramana Maharshi for study by seekers. It is like a dialogue between Lord Dattatreya and Sage Parasurama. The following excerpts are from the book that was translated in English by  Munagala Venkataramiah (Swami Ramanananda Saraswathi).
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"Tripura literally means the three cities. They are the states — Jagrat, svapna and Sushupti. The undercurrent of consciousness in all of them,  remaining unaffected, is metaphorically called the Resident Mistress by  name Sri Tripura. The procreative faculty generating 

new beings and the link of altruistic love connecting the 

offspring to the parent are personified in the Mother. Hence 

the feminine termination of Tripura." - From Tripura Rahasya

Sage Parasurama said,

• Sri Guru! Ocean of Mercy, can anyone drenched with Thy kindness ever be afflicted by ailments, even if destiny so decree?
• How can the burning pains of illness touch one who is abiding in the refreshing moon of Thy nectar-like kindness?
• I feel happy in body and mind, being refreshed by Thy kindness. Nothing afflicts me except the desire to remain in unbroken contact with Thy holy feet. The very sight of Thy holy feet has made me perfectly happy, but there are a few long-standing doubts in my mind.
• With Thy kind permission I desire to propound them.
• Hearing the words of Parasurama, Dattatreya, the Ocean of Kindness, was pleased and said to him:
• Ask at once, O Bhargava, what you so much want to know and what you have so long been thinking about. I am pleased with your devotion and shall answer your questions with pleasure.

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Excerpts from Chapter 1, Tripura Rahasya