But implicit in your question of “where did that come from” is that there was a time before the universe existed when there was nothing. But time did not exit prior to the big bang
(speculation that insinuates the SUPERnatural) so your question becomes meaningless; there was no “before”
(speculation that insinuates the SUPERnatural) . This idea of time coming into existence with the 3 spatial dimensions is not just a convenient invention to avoid having to answer questions like yours, it is a fundamental conclusion based on physical principles
(speculation that insinuates the SUPERnatural) .
And once again, I remind you that physics can handle what happened down to a blink of time after the big bang, but in that first primordial blink, all of our physics breaks down
(speculation that insinuates the SUPERnatural) . “We don’t know” is a perfectly truthful answer for a lot of questions in science, and an understanding of the first moment after the big bang is in that category.
So if you need to posit “an uncaused supernatural cause” as the “only plausible answer” go ahead
(ThePhy is also positing an "uncaused cause") . Others prefer invisible pink elephants under their bed, and have equal proof of their correctness. Personally, I don’t find much comfort in inventing psychological placebos like “uncaused causes”
(except in this post ) .