Stephenson:Neal:The System of the World:886:The journey began with a wizard walking into his door (PaulJ)

From the Quicksilver Metaweb.

This is a reference/wink/homage to Tolkien's The hobbit.

There are plenty of other references to "The Hobbit" in The System of the World, including the ring Daniel is given from Solomon Kohan "weighing heavily" in his pocket during a conversation with Newton in the Clubb, and a howitzer gun that is referred to as a "Hobbit" by the author.