The etiquette of praising a fellow Muslim

When a man began to praise another in his presence, the Messenger of Allah ﷺ exclaimed: "Woe to you, you have cut your companion's neck!"¹ Then he said: "If any of you must praise his brother, let him say:"

"I reckon so-and-so [is such], but Allah knows him best; I do not extol anyone before Allah² — I reckon him to be such and such — if indeed you know that of him."

¹ Meaning that excessive praise can destroy the one praised by filling him with pride. ² That is, I do not vouch for his state before Allah.

[al-Bukhari 2662; Muslim 3000]