BERTIE Ahern believed two unexplained cheques totalling IR£10,000 were political donations -- but said one of these was for his own "personal use".
And he now claims the other cheque came from one of his brothers following the death of his father.
However, Mr Ahern admitted he never paid any tax on these donations.
The money was lodged to his savings account in 1994 and 1995, but he only told the Revenue Commissioners about the payments in recent years.
Mr Ahern admitted he could not be absolutely certain where the monies came from, despite having trawled through his financial records back to the 1980s.
The Planning Tribunal heard the two cheques, each for IR£5,000, were lodged to Mr Ahern's Irish Permanent Building Society account in January 1994 and December 1995.
But apart from a building society document showing the lodgments, there were no other records to check what the source of the lodgments were.
Mr Ahern had told the inquiry he had opened the building society account for the purpose of looking for a mortgage.
Asked to explain where the funds had come from, he said he believed one was a donation from a company, while the second may have been from a family member.
Mr Ahern said he had trawled through his financial records to try to match up the payments and he thought one of the cheques had come from a company.
He had gone to that company three or four times to check if the payment did come from there.
But the company could not verify the individual he thought had given the money had in fact done so.
Mr Ahern believes the person who gave him the cheque is now dead.
He said he believed that the cheque had been given as a "political donation for my personal use".
But Mahon Tribunal lawyer Des O'Neill asked what reason could there be for lodging such funds to an account Mr Ahern was using to buy a house.
"If they gave me the money for my personal use that is the only way I would do that, otherwise I would give it to my party," he said.
Mr O'Neill said if it was the case he had received a gift of that amount in 1994 it would have carried a tax implication but Mr Ahern did not make a return in relation to the amount at that time.
The Taoiseach agreed he had not.