"The Congress party is desperate. Mala fide and defamatory allegations have been levelled against the son of the BJP president. Even that website has never said there is any illegality," he told a press meet here.
The law minister claimed that the news website -- The Wire -- which published the story on Shah's son Jay Amit Shah's business dealings, arrived at a wrong conclusion on the basis of evidence and reasoning.
Prasad justified the law ministry's decision to grant permission to Additional Solicitor General Tushar Mehta to give legal advice to Jay Shah in the case.
"It is a private dispute, in which the Government of India is not a party," he said, while responding to a query.
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The BJP leader also hit out at Rahul Gandhi, a day after the Congress vice-president took a swipe at Prime Minister Narendra Modi, pressing the latter to "say something" on the claims in the report published by the website.
Prasad also said that the Congress vice-president had never uttered a word about his brother-in-law, Robert Vadra's business transactions.
Meanwhile, a group of Congress workers burned an effigy of Amit Shah at Kollam and demanded a probe into the business dealings of his son.