'Do you know what is backbiting?'
They (the Companions) said: 'Allah and His Messenger (saws) know best.' Thereupon he (the Prophet (peace be upon him)) said:
'Backbiting implies your talking about your brother (behind his back) 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 (peace be upon him) said: 'If (that failing) is actually found (in him) what you assert, you in fact backbitten him, and if that is not in him it is a slander.'
The above quotation was said by Prophet Muhammad (peace be upon him) Sahih Muslim Hadith 6265 Narrated by Abu Hurayrah