The daily sitting had just convened with Najib answering a question about the Government's long-term measures to manage the national economy when Azmin (PKR-Gombak) stood to ask a supplementary question.
He quoted an international news report last month, which stated that Malaysia had spent 12.5% of its revenue on interest payments for the national debt in 2016 compared to 9% in 2009.
"The report says that this year we are expected to spend RM31bil of revenue just to pay interest, and this is the same as two-thirds of (the total) GST collection.
Has the 1MDB debt issue affected the rise in our debt interest, or is there a more responsible reason for this?" asked Azmin, causing murmurs in the House.
Azmin then called on the MPs to let Najib have the chance to answer.
Najib then stood up to respond and calmly said "the water issue in Selangor is even more critical".
Azmin immediately stood up to protest, saying that the response had nothing to do with the issue of national debt.
A shouting match ensued in the Dewan when Barisan Nasional MPs – including Datuk Seri Abdul Azeez Rahim (Baling) and Datuk Othman Abdul (Pendang) – asked Azmin to sit down.
Speaker Tan Sri Pandikar Amin Mulia intervened and ordered Azmin to take a seat and for other MPs to remain silent.
"This is the specialty of Parliament, when there are questions there will be answers. Sometimes the question carries a different meaning, so when the answer is given naturally there will be a different meaning," said Pandikar.
"This is what we call politics, but this should not go to a stage where the Standing Orders are contravened.
The question was if 1MDB's debt situation was critical, and the answer was that the Selangor water issue was more critical," he added.
Pandikar also warned Azmin that he would exercise his power as Speaker if Azmin stood up in protest again.
Najib then explained that it was not a question of the quantum of national debt, but the ability to repay it.
"Singapore's national debts are bigger than ours and their repayment abilities are also existent.
"Our ability to repay is unquestionable and international rating agencies have put us in the top categories. Our national debt is managed well. Hopefully, the Selangor water issue will also be settled properly," he said.