Buhari had justified the withdrawal of the money, saying FG needed to beat the US deadline for the purchase of the aircraft.
After the withdrawal, Buhari had written a letter to the Senate seeking the approval of the legislature for the withdrawal of $496 million from the ECA.
However, he noted in the letter that the money had been withdrawn and paid to the United States for the 12 Super Tucano aircraft, ahead of legislative approval.
The President said he did this to beat the deadline for the arms deal. The planes are expected to be delivered in 2020.
At the plenary on Wednesday, April 25, 2018, Senate President Bukola Saraki read the President's letter and lawmakers berated Buhari for allegedly breaking the law.
The President's letter read in part, "Recently, approval was granted by the United States government, but with a deadline, within which part payment must be made otherwise the contract relapses.
"In the expectation that the National Assembly will have no objection to the purchase of these highly specialised aircraft, which is critical to national security, I granted anticipatory approval for the release of $496,374,470.
"This was paid directly into the treasury of the United States government.
"I am therefore writing, seeking approval of the Senate for the sum of $496,374,470 (equivalent to N151,394, 421,035) to be included in the 2018 Appropriation Bill which the National Assembly is currently finalising.
"The balance for the requirement for critical operational equipment is still being collated from the different security services and will be presented in the form of a supplementary appropriation bill in due course."
Raising a point of order, Senator Mathew Uroghide (PDP, Edo-South) declared Buhari's action illegal.
Uroghide said in part, "I heard very clearly when you read the letter that came from Mr. President over the payment that was made for the Tucano aircraft. I was completely taken aback because I represent a people.
"This letter that you just read to us now, with due respect to the office and the status of Mr. President, I want to say that what he just said, which you just read to us, is a violation of some of the provisions of the Constitution.
"I stand on it with every vehemence and I want to read Section 80 (1),(2),(3) and (4) of the Constitution."
The lawmaker read the sections of the Constitution he made reference to.
He further said, "what you just read to us violates these provisions. Mr. President couldn’t have ever, and no Nigerian citizen that is up and active under the provisions of the Constitution, is allowed to make any disbursement or any approval coming from any quarter, whether it is by the Council of State of the Federation or the committee of the governors or anybody in the Presidency, without approval or appropriation from this Assembly.
"I think it important that we remind ourselves, because if we sit down here, tomorrow, posterity will judge us."
Responding to Uroghide's comments, Saraki admitted that the lawmaker raised a valid point but noted that the matter will be taken at another time.
Saraki also indicated that the matter might be raised at the next legislative day (Thursday, April 26) based on its importance and urgency.