Tirmidhi Book 27, Hadith 1934

حَدَّثَنَا قُتَيْبَةُ، حَدَّثَنَا عَبْدُ الْعَزِيزِ بْنُ مُحَمَّدٍ، عَنِ الْعَلَاءِ بْنِ عَبْدِ الرَّحْمَنِ، عَنْ أَبِيهِ، عَنْ أَبِي هُرَيْرَةَ قَالَ:‏‏‏‏ قِيلَ:‏‏‏‏ يَا رَسُولَ اللَّهِ، ‏‏‏‏‏‏مَا الْغِيبَةُ ؟ قَالَ:‏‏‏‏ ذِكْرُكَ أَخَاكَ بِمَا يَكْرَهُ ، ‏‏‏‏‏‏قَالَ:‏‏‏‏ أَرَأَيْتَ إِنْ كَانَ فِيهِ مَا أَقُولُ ؟ قَالَ:‏‏‏‏ إِنْ كَانَ فِيهِ مَا تَقُولُ فَقَدِ اغْتَبْتَهُ، ‏‏‏‏‏‏وَإِنْ لَمْ يَكُنْ فِيهِ مَا تَقُولُ فَقَدْ بَهَتَّهُ ، ‏‏‏‏‏‏قَالَ:‏‏‏‏ وَفِي الْبَابِ عَنْ أَبِي بَرْزَةَ، ‏‏‏‏‏‏وَابْنِ عُمَرَ، ‏‏‏‏‏‏وَعَبْدِ اللَّهِ بْنِ عَمْرٍو، ‏‏‏‏‏‏قَالَ أَبُو عِيسَى:‏‏‏‏ هَذَا حَدِيثٌ حَسَنٌ صَحِيحٌ.

Abu Hurairah narrated that it was said: O Messenger of Allah! What is backbiting? He said : Mentioning your brother with that which he does not like. He said What if what I said about him is so? He said: If what you said about him is so, then you have backbitten him, and if it is not as you said, then you have slandered him.