Good Manners and Form (Al-Adab)
Ṣaḥīḥ al-Bukhārī 6162
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
waylaka qaṭaʿta ʿunuqa akhīka thalāthan man kāna minkum mādiḥan lā maḥālaha falyaqul aḥsibu fulānan wallāh ḥasībuhu walā uzakkī ʿalā-Llāh aḥadan. in kāna yaʿlamu
Transliteration generated from the Arabic vowel marks
The full narration
Narrated Abu Bakra: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)
Source
Ṣaḥīḥ al-Bukhārī · 6162