The concept of Basic Structure was introduced by the Supreme Court in which of the following cases?

On the question whether the amending power under article 368 was absolute and unlimited, seven judges constituting a majority held that the amending power under article 368 was subject to an implied limitation. By a majority of 7 to 6, the court ruled that “Article 368 does not enable the Parliament to alter the basic structure or framework of the Constitution” without specifying what the basic structure of the Constitution was.