From a column in the San Bernardino Sun comes a somewhat unlikely claim:

To determine the origin of this mirror-breaking business, I first consulted the Old Farmers Almanac. The superstition about breaking mirrors began with the ancient Romans, who supposedly saw their souls while looking at themselves in gazing pools, states the long-trusted resource. If someone threw a stone into a pool, breaking up a gazer's image, it meant seven years of bad luck for the gazer.

Anyone have a source for this?