Step 1: Understanding the Concept:
The question is about the legalization of passive euthanasia in India. Euthanasia is the practice of intentionally ending a life to relieve pain and suffering. It is distinguished into "active" (ending life through an act, like a lethal injection) and "passive" (withholding or withdrawing life-sustaining treatment). The question asks for the landmark case that permitted passive euthanasia.
Step 2: Detailed Explanation:
Let's trace the jurisprudence:
\begin{itemize}
\item P. Rathinam v. Union of India (1994): The Supreme Court held that the 'right to life' under Article 21 includes the 'right not to live', i.e., the right to die, and decriminalized Section 309 IPC (attempt to commit suicide).
\item Gian Kaur v. State of Punjab (1996): A larger constitutional bench overruled the \textit{P. Rathinam} decision. It held that the 'right to life' does not include the 'right to die'. It, however, observed that the right to life includes the right to a dignified life up to the point of death, including a dignified procedure of death, hinting at the permissibility of passive euthanasia.
\item Aruna Ramachandra Shanbaug v. Union of India (2011): This was the landmark case where the Supreme Court explicitly legalized passive euthanasia. The case involved Aruna Shanbaug, a nurse who had been in a persistent vegetative state for decades. While the court did not grant euthanasia in her specific case, it laid down a comprehensive legal framework and guidelines for allowing passive euthanasia for patients who are terminally ill or in a persistent vegetative state. It held that the right to a dignified death is a part of the right to life under Article 21. This was later given statutory backing by the Supreme Court in \textit{Common Cause v. Union of India (2018)}.
\end{itemize}
Step 3: Final Answer:
The principle that "Passive Euthanasia is permitted in certain cases" was decisively held in Aruna Ramachandra Shanbaug Vs. Union of India.