Using an existing icon for a new plugin?

I've written a plugin called AjaxSave. How can I make its toolbar button use the regular save icon?

Apparently this forum disables .txt attachments!?? Plugin pasted below. To use it, throw something like this into your config:

var config = {
    on: { save: function (evt) { evt.editor.destroy() } }
}

This is just until a proper solution can be found for this issue: http://dev.fckeditor.net/ticket/4507

(function()
{
    var saveCmd =
    {   
        modes : { wysiwyg:1, source:1 },

        exec : function( editor )
        {       
            editor.fire('save');
        }       
    };  

    var pluginName = 'ajaxsave';

    CKEDITOR.plugins.add( pluginName,
    {   
        init : function( editor )
        {       
            var command = editor.addCommand( pluginName, saveCmd );

            editor.ui.addButton( 'AjaxSave', 
                {               
                    label : editor.lang.save, 
                    command : pluginName
                });             
        }       
    }); 
})();