Mr Ahern is taking a legal challenge against the inquiry
Lawyers for Taoiseach Bertie Ahern have accused the Mahon Tribunal into alleged planning corruption of withholding information from them.
Bertie Ahern has been giving evidence about his personal finances in the 1990s.
It is the third time he has done so in the last six months.
Mr Ahern is taking a legal challenge against the inquiry asking him questions over statements he has made in the Dail.
He contests that these are protected by constitutional privilege.
Mr Ahern told Thursday's hearing that a payment into his bank account in the 1990s may have been inheritance money from his late father, but he had no record of it.
He said he received inheritance payments at the time from his brother after the death of their father.
However, he could not establish if this was the source of the money because he could not trace the cheque.
"I can positively tell you I got IR£5,000 from my family. A brother of mine gave me IR£5,000 he had from my father," he said.
Addressing tribunal chairman Judge Alan Mahon, Mr Ahern asked: "Do I have to explain how my mother and father dealt with their affairs."
Judge Mahon replied: "We don't want to ask you to explain those details in public."