Bulugh al-Maram, Book 16, Hadith 1538 (English) ⓘ

Abu Hurairah (RAA) narrated, ‘The Messenger of Allah asked, “Do you know what backbiting is?” They replied, `Allah and His Messenger know best.’ He said, “It is saying something about your brother which he dislikes.” Someone asked, ‘Supposing that what I said about my brother was true?’ and the Messenger of Allah said: “If what you say about him is true you have backbitten him and if it is not true you have slandered him.” Related by Muslim.

وَعَنْ أَبِي هُرَيْرَةَ ‏- رضى الله عنه ‏- أَنَّ رَسُولَ اَللَّهِ ‏- صلى الله عليه وسلم ‏-قَالَ: { أَتَدْرُونَ مَا اَلْغِيبَةُ?