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. (Using translation from Muslim 3000a)
مَدَحَ رَجُلٌ رَجُلًا عِنْدَ النَّبِيِّ ﷺ فَقَالَ وَيْلَكَ قَطَعْتَ عُنُقَ صَاحِبِكَ مِرَارًا إِذَا كَانَ أَحَدُكُمْ مَادِحًا صَاحِبَهُ لَا مَحَالَةَ فَلْيَقُلْ أَحْسِبُ فُلَانًا وَاللهُ حَسِيبُهُ وَلَا أُزَكِّي عَلَى اللهِ أَحَدًا أَحْسِبُهُ إِنْ كَانَ يَعْلَمُ ذَاكَ كَذَا وَكَذَا