The Book of Zuhd and Softening of Hearts
Ṣaḥīḥ Muslim 7501
إِذَا كَانَ أَحَدُكُمْ مَادِحًا صَاحِبَهُ لاَ مَحَالَةَ فَلْيَقُلْ أَحْسِبُ فُلاَنًا وَاللَّهُ حَسِيبُهُ وَلاَ أُزَكِّي عَلَى اللَّهِ أَحَدًا أَحْسِبُهُ إِنْ كَانَ يَعْلَمُ ذَاكَ كَذَا وَكَذَا
idhā kāna aḥadukum mādiḥan ṣāḥibah lā maḥālaha falyaqul aḥsibu fulānan wallāh ḥasībuhu walā uzakkī ʿalā-Llāh aḥadan aḥsibuhu in kāna yaʿlamu dhāka kadhā wakadhā
Transliteration generated from the Arabic vowel marks
The full narration
Abd al-Rahman b. Abu Bakra reported on the authority of his father that a person praised another person in the presence of Allah's Apostle (ﷺ), whereupon he said:Woe be to thee, you have broken the neck of your friend, you have broken the neck of your friend-he said this twice. If one of you has to praise his friend at all, he should say: I think (him to be) so and Allah knows it well and I do not know the secret of the heart and Allah knows the destined end, and I cannot testify his purity against Allah but (he appears) to be so and so
Source
Ṣaḥīḥ Muslim · 7501