Napoleon Series Archive 2003

Napoleon to Josephine -- Don't wash?

The quotation "Je reviens en trois jours, ne te laves pas" is often attributed in the popular literature to a letter of Napoleon to Josephine, urging the empress to maintain her natural body odor. Though this appears scores of times and supposedly lent a moniker to a perfume (Je reviens), I can't find an actual reference to a known letter of Napoleon. Does anyone know if this was actually written by him, and if so, when?
Many thanks.