Hadith 2749
It is narrated from Sayyiduna Abu Hurairah (may Allah be pleased with him): The Noble Prophet (peace and blessings be upon him) was asked, "What is backbiting?" He replied, "Backbiting is that you mention about your brother something which he dislikes." It was asked, "What if that fault is actually present in my brother?" He (peace and blessings be upon him) said, "If what you say is present in him, then you have backbitten him, and if it is not present in him, then you have slandered him."