The Concept of "Slander" In Islam

From Will at The Other News:

The Reliance of the Traveller (or ‘Umdat al-Salik’) maintains that slander (ghiba) includes the mention of anything concerning a person [i.e., a Muslim] “that he would dislike.” This discussion also cites a canonical hadith which contains the following account:

“Do you know what slander is?” They answered, “Allah and His Messenger know best.” He said, “It is to mention of your brother that which he would dislike.” Someone asked, “What if he is as I say?” And he replied, “If he is as you say, you have slandered him, and if not, you have calumniated him.”