Swamy claimed that Pakistan's ISI has information on black money stashed abroad by Indian politicians and that this was the reason why India hasn't been taking a tough stand on cross-border terrorism. "It is exactly for this reason that those in power are hemming and hawing on the issue of sending Afzal Guru and Ajmal Kasab to gallows,'' he said. don't speak without evidence. This has been my record. However, I need not furnish proof to you,'' he retorted when a media-person asked him if he had proof of Indian politicians being blackmailed by the ISI on the hawala issue. http://articles.timesofindia.indiatimes.com/2012-02-06/mumbai/31030059_1_subramanian-swamy-hawala-issue-black-money
So where and from whom did Swamy gather such proofs?
From News Archives, July 2011: FBI arrests Pakistani-American Nabi Fai on charges of secretly funneling at least $4 million from Pakistan's top spy agency ISI into American political activities, aiming to influence US policy on Kashmir.
Janata Party president Subramanian Swamy on Thursday clarified that when he participated in a seminar in 2003 on Kashmir, organised by an organisation run by U.S.-based Kashmir activist Ghulam Nabi Fai, he was unaware that Dr. Fai was an “undercover agent of a foreign power.” In a statement, Dr. Swamy said he delivered an address on Kashmir in the seminar held in the U.S. Senate Building in Washington in the summer of 2003. At that time, he was teaching economics at the Harvard University. He had checked with the Indian Embassy about the organisers and was told that ‘it was an anti-Indian gathering but not that it was ISI-inspired.” Dr. Swamy said his friends also did not know that Dr. Fai was working for the ISI but had assumed that a meeting at the Senate Building would not have been permitted without security clearance. He had, however, requested the Embassy to send an official with him to take notes and for consultations. His speech had since been published in the print media in India and that it made the point Kashmir was part of India. “It is impossible to know unless briefed who is an undercover agent of a foreign power.”http://www.thehindu.com/news/national/article2282617.ece
P.S. Don't let your imagination fire like that of Swamy's