What is the probability of finding an electron in a hydrogen atom in an infinitesimal space $dV$?

I have been asked to find the most probable position of electron in infinitesimal space $dV$ orbiting a Hydrogen atom. I know that probability $P$ of finding the electron in a volume $dV$ is given by
$$
P = |psi(vec r,t)|^2 dV
$$
where $psi(vec r,t) = A e^{-r/a_0}e^{-iE_1t/bar{h}}$.

The time dependence is irrelevant and this gives me
begin{align}
P &= |A|^2e^{-2r/a_0}dV
&= |A|^2e^{-2r/a_0}d^3r
&= |A|^2e^{-2r/a_0}[r^2 sin(theta)dr, dtheta, dphi]
end{align}
My question is what do I do next? When I differentiate it by $dr$ it will give me $a_0$, but that represents the spherical shell where the probability is highest. Not infinitesimal space with the highest probability.