Silsilah Sahihah

It is narrated Mursal from Sayyiduna Mutalib bin Abdul Malik bin Hantab that a man asked the Messenger of Allah (peace and blessings be upon him): "What is backbiting?" The Messenger of Allah (peace and blessings be upon him) said: "To mention something about a person which he dislikes to hear." He said: "O Messenger of Allah! Even if that thing is true (and correct)?" The Messenger of Allah (peace and blessings be upon him) said: "If you have said something untrue (about someone), then that is slander (not backbiting)."

Amr bin Shu'aib narrates from his father, who narrates from his grandfather, and he from Sayyiduna Mu'adh bin Jabal (may Allah be pleased with him), that he said: The companions mentioned a man to the Messenger of Allah (peace and blessings of Allah be upon him), saying: He does not eat until he is fed, and he does not ride until he is made to ride. The Prophet (peace and blessings of Allah be upon him) said: "You have backbitten him." The companions said: O Messenger of Allah! We only mentioned (the fault) that is present in him. He (peace and blessings of Allah be upon him) said: "(For backbiting) it is sufficient that you mention about your brother that (fault) which is in him."