How to "update_attributes" without executing "before_save"?

I have a before_save in my Message model defined like this:

   class Message < ActiveRecord::Base
     before_save lambda { foo(publisher); bar }
   end

When I do:

   my_message.update_attributes(:created_at => ...)

foo and bar are executed.

Sometimes, I would like to update message's fields without executing foo and bar.

How could I update, for example, the created_at field (in the database) without executing foo and bar ?