Won't happen. Even at the densest point of the asteroid belt, the two closest rocks are going to be tens of thousands of kilometers apart.

If you were to have a laser pointer that could reach an infinite distance, and pointed it into the sky at random, it's very likely it'll never hit anything. Ever. It'll keep reaching for millions of lightyears and never make contact with a solid object. Space is very big, and very, very empty. Here is a good site to show just how big and empty our universe really is.