The sources said Bansal was called at 11am to CBI guest house, located five kilometers from the agency's headquarters, to avoid the media which gathered outside its headquarters.
They said he was grilled till 6.45 in the evening with a break of about one and a half hours in between for lunch.
The sources said CBI wants to examine the role of Bansal, if any, in the alleged bribery scandal.
Bansal was asked a number of questions about his meetings with Kumar, his promotion as Board member and the additional charge given to him as General Manager (West).
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The duo were taken into custody by CBI on May 3 when it nabbed Singla with Rs 90 lakh alleged bribe money.
The sources claimed the agency confronted Bansal with phone conversation intercepts, call detail records and grilled him on how Singla was able to assure Kumar about his elevation if he had not discussed the matter with him.
The Chandigarh MP denied having knowledge of having any deal struck between Singla and Kumar. He also claimed his innocence in the entire scandal and said he had not given any assurance to Kumar about his elevation as Board Member, the sources said.