The UVic Writer's Guide

One Of Two Or More Works By The Same Author(s)

If it is clear which author you are discussing, simply put the work, or a recognisable abbreviation of it.

(Work Location)

(Lear 2.3.121)

("To Margaret Taylor" 630)

Otherwise separate the author and the work (or abbreviation of it) by a comma, then as usual a space and the reference:

(Author,Work Location)

(Austen, Northanger Abbey 113)

(MacLuhan, "Pound" 559)