Sahih al-Bukhari 6162
Sahih al-Bukhari · Book 78: Good Manners and Form (Al-Adab) · Saying "Wailaka."
Narrated Abu Bakra:
حَدَّثَنَا مُوسَى بْنُ إِسْمَاعِيلَ ، حَدَّثَنَا وُهَيْبٌ ، عَنْ خَالِدٍ ، عَنْ عَبْدِ الرَّحْمَنِ بْنِ أَبِي بَكْرَةَ ، عَنْ أَبِيهِ ، قَالَ أَثْنَى رَجُلٌ عَلَى رَجُلٍ عِنْدَ النَّبِيِّ صلى الله عليه وسلم فَقَالَ " وَيْلَكَ قَطَعْتَ عُنُقَ أَخِيكَ ـ ثَلاَثًا ـ مَنْ كَانَ مِنْكُمْ مَادِحًا لاَ مَحَالَةَ فَلْيَقُلْ أَحْسِبُ فُلاَنًا ـ وَاللَّهُ حَسِيبُهُ ـ وَلاَ أُزَكِّي عَلَى اللَّهِ أَحَدًا. إِنْ كَانَ يَعْلَمُ ".
A man praised another man in front of the Prophet. The Prophet (ﷺ) said thrice, "Wailaka (Woe on you) ! You have cut the neck of your brother!" The Prophet (ﷺ) added, "If it is indispensable for anyone of you to praise a person, then he should say, "I think that such-and-such person (is so-and-so), and Allah is the one who will take his accounts (as he knows his reality) and none can sanctify anybody before Allah (and that only if he knows well about that person.)".