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 ﷺ 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)).