Muwatta Imam Malik Book of Speech, Hadith 10

Malik related to me from al-Walid ibn Abdullah ibn Sayyad that al-Muttalib ibn Abdullah ibn Hantab al-Makhzumi informed him that a man asked the Messenger of Allah ﷺ "What is backbiting?" The Messenger of Allah ﷺ said, "It is to mention about a man what he does not want to hear." He said, "Messenger of Allah! Even if it is true?" The Messenger of Allah ﷺ said, "If you utter something false, then it is slander."

حَدَّثَنِي مَالِكٌ، عَنِ الْوَلِيدِ بْنِ عَبْدِ اللَّهِ بْنِ صَيَّادٍ، أَنَّ الْمُطَّلِبَ بْنَ عَبْدِ اللَّهِ بْنِ حَنْطَبَ الْمَخْزُومِيَّ، أَخْبَرَهُ أَنَّ رَجُلاً سَأَلَ رَسُولَ اللَّهِ ﷺ مَا الْغِيبَةُ فَقَالَ رَسُولُ اللَّهِ ﷺ " أَنْ تَذْكُرَ مِنَ الْمَرْءِ مَا يَكْرَهُ أَنْ يَسْمَعَ " . قَالَ يَا رَسُولَ اللَّهِ وَإِنْ كَانَ حَقًّا قَالَ رَسُولُ اللَّهِ ﷺ " إِذَا قُلْتَ بَاطِلاً فَذَلِكَ الْبُهْتَانُ " .