You may therefore be answered as follows:
The impossible regress is a regress in causes and in what makes them complete. As for a regress in conditions or effects, Muslims hold two views, whereas you maintain that it is possible.
We therefore say: Either this regress is possible or it is impossible. If it is impossible, an infinite succession of temporally originated things is impossible, and they must have a beginning. Your assertion that there are temporally originated things without a beginning is thus invalidated, and the movements of the celestial spheres cannot have existed from eternity. This refutes your position.
We then say: If the world had existed from eternity, either it would always have contained temporally originated things—whether these are said to arise in a body or an intellect—or it would have contained nothing temporally originated in eternity, as when it is said to have been a motionless body. The first alternative would entail an infinite succession of temporally originated things. Since we are considering the supposition that such a succession is impossible, this alternative is ruled out. If, however, temporally originated things arose within it after not having existed, it would follow that they can proceed from something eternal that has undergone no change. This invalidates your argument and entails that temporally originated things can arise without a cause coming into being.
If you say that an infinite regress in effects is possible—which is indeed your position—then your use of this argument to establish the eternity of anything in the world is invalid. It does not establish the eternity of any particular thing in the world; it establishes only that the Lord is perpetually active.
You may then be asked: Why could the celestial spheres, or whatever is posited as existing in the world, or everything Allah brings into being, not depend upon one temporally originated thing after another, with the entire world as it now exists being like a single individual among other temporally originated individuals?
It thus becomes clear that your argument for the conclusion you seek is invalid, whether an infinite succession of temporally originated things is possible or not. Indeed, if it is not possible, both the argument and the position for which you are known are invalidated,