كتاب الأمور المنهي عنها
18
The Book of the Prohibited actions
Abu Hurairah (May Allah be pleased with him) said:
The Messenger of Allah (ﷺ) said, "Do you know what is backbiting?" The Companions said: "Allah and His Messenger know better." Thereupon he said, "Backbiting is talking about your (Muslim) brother in a manner which he dislikes." It was said to him: "What if my (Muslim) brother is as I say." He said, "If he is actually as you say, then that is backbiting; but if that is not in him, that is slandering."

[Muslim].

وعن أبي هريرة رضي الله عنه أن رسول الله صلى الله عليه وسلم قال‏:‏ “أتدرون ما الغيبة‏؟‏” قالوا‏:‏ الله ورسوله أعلم قال‏:‏ ‏"‏ذكرك أخاك بما يكره‏"‏ قيل‏:‏ أفرأيت إن كان في أخي ما أقول‏؟‏ قال‏:‏ ‏"‏إن كان فيه ما تقول، فقد اغتبته، وإن لم يكن فيه ما تقول فقد بهته”‏.‏ ‏(‏‏(‏رواه مسلم‏)‏‏)‏‏.‏
Sunnah.com reference : Book 18, Hadith 13
Arabic/English book reference : Book 18, Hadith 1523