Sahih Muslim Book - 53, Hadith - 7501

حَدَّثَنَا يَحْيَى بْنُ يَحْيَى حَدَّثَنَا يَزِيدُ بْنُ زُرَيْعٍ عَنْ خَالِدٍ الْحَذَّاءِ عَنْ عَبْدِ الرَّحْمَنِ بْنِ أَبِى بَكْرَةَ عَنْ أَبِيهِ قَالَ مَدَحَ رَجُلٌ رَجُلاً عِنْدَ النَّبِىِّ -صلى الله عليه وسلم- - قَالَ - فَقَالَ « وَيْحَكَ قَطَعْتَ عُنُقَ صَاحِبِكَ قَطَعْتَ عُنُقَ صَاحِبِكَ ». مِرَارًا « إِذَا كَانَ أَحَدُكُمْ مَادِحًا صَاحِبَهُ لاَ مَحَالَةَ فَلْيَقُلْ أَحْسِبُ فُلاَنًا وَاللَّهُ حَسِيبُهُ وَلاَ أُزَكِّى عَلَى اللَّهِ أَحَدًا أَحْسِبُهُ إِنْ كَانَ يَعْلَمُ ذَاكَ كَذَا وَكَذَا ».

It was narrated from 'Abdur-Rahman bin Abi Bakrah that his father said: "A man praised another man in the presence of the Prophet (s.a.w). He said: 'Woe to you, you have cut your companion's neck, woe to you, you have cut your companion's neck,' (and he, (s.a.w) said it) several times. (Then continued) 'If one of you must praise his companion, let him say: "I think that so-and-so is such and such, but Allah knows best and I do not confirm anyone's good conduct before Allah."'