There would have to be an ultimate basis, whether QM, actual stuff, 'nothing', or whatever, for cause and effect cannot go on forever, as not only would this be an infinite regress, but, practically, it would mean that the effect would take forever to result from the cause, never arriving.
So, 'forever there' is likely for the basis, plus perhaps even that this causeless prime mover should be infinite and everywhere as well as eternal, for what else would there be around. Yes, religion and science do seem to converge on some points, but then diverge, for there's nothing that can be prior to mindfully impose order on a causeless state, or even unmindfully, unless one proposes some brute force happenings that 'try' everything, such as QM taking all paths, in superposition, which is still not a God, but just the land of the law of no laws.