hadith

 Sahih Bukhari  صحیح بخاری

Hadith # 2662

Translation:

Narrated Abu Bakra (RA): 

A man praised another man in front of the Prophet ﷺ . The Prophet ﷺ said to him, "Woe to you, you have cut off your companions neck, you have cut off your companions neck," repeating it several times and then added, "Whoever amongst you has to praise his brother should say, I think that he is so and so, and Allah knows exactly the truth, and I do not confirm anybodys good conduct before Allah, but I think him so and so, if he really knows what he says about him."