Abu Huraira (ra) reported Allah's Messenger (saw) as saying: ‘Do you know what is backbiting?’  They (the Companions) said:  ‘Allah and His Messenger (saw) know best.’ Thereupon he (the Holy Prophet saw) said:  ‘Backbiting implies you talking about your brother in a manner which he does not like.’  It was said to him:  ‘What is your opinion about this that if I actually find (that failing) in my brother which I made a mention of?’  He said (saw):  ‘If (that failing) is actually found (in him) what you assert, you in fact have backbitten him, and if that is not in him it is a slander.’ (Sahih Muslim )