It is out of the question

What exactly is outside the question? What was the question?..

Dad, can I borrow your car to go to the pub with my mates

…might be the type of question that could evoke a response like that, meaning

No with a capital N.

So if that is the question, what is outside it? We sent our team out to investigate.

It would appear that ‘question’ here is not the original one but it being ‘out of ..’  means that the subject is not open to futher discussion so no more questions will be considered.

Of course that’s what it is, bleedin’ obvious in’it.

According to Christine Ammer of The American Heritage® Dictionary of Idioms the phrase dates back the the 1700’s.