Broadcaster Eamon Dunphy has testified he was told that Taoiseach Bertie Ahern was 'taken care of' to support a shopping centre development in the 1990s.
Mr Dunphy said he cannot say where or exactly when the conversation with developer Owen O'Callaghan took place, but he thinks it was in Dublin.
It was between 1997 and 1998 when the two men were involved in a project to bring Wimbledon FC to Dublin.
He said Mr O'Callaghan referred to his Golden Island Shopping Centre development in Athlone.
He said Mr O'Callaghan told him that then Minister for Finance, Bertie Ahern, was 'taken care of' to support tax designation for the site but did not deliver on the deal.
Mr Dunphy said he took this to mean Mr Ahern received a bribe.
But under questioning he said if Mr O'Callaghan said this inference was mistaken he would accept it.
Mr Dunphy said he had not questioned Mr Ahern's integrity, specifically during an appearance on the Late Late Show before last year's general election. He said he did not think the allegation was particularly striking in the overall scheme of things.
He said the conversation with Mr O'Callaghan was confidential and he was not wearing his journalist hat at the time.
But he said after dastardly allegations were made against his friend, journalist Frank Connolly, under Dáil privilege, iron entered his soul and this was a factor in deciding to make a statement when asked by the tribunal.
But he denied making up the allegation for revenge against Bertie Ahern.
He told counsel for Owen O'Callaghan 'if you are suggesting for one minute I would come to this tribunal and perjure myself, and damage the Taoiseach and a businessman for who I have the highest regard, to wreak revenge for Frank Connolly…you must be mad'.
Meanwhile, the Taoiseach has denied Fine Gael claims that his legal challenge to the Mahon Tribunal will delay its work for up to six months.
Mr Ahern told reporters that the tribunal has been going on for 11 years and he did not think he had caused it any delay.
He said he was ready to give evidence to the tribunal next week, as scheduled.