Woe unto you! You have cut the neck of your companion
Authentic hadithعن أبي بكرة رضي الله عنه : أن رجلًا ذكر عند النبي صلى الله عليه وسلم فأثنى عليه رجلٌ خيرًا، فقال النبي صلى الله عليه وسلم : «ويحك! قطعت عنق صاحبك» يقوله مرارًا: «إن كان أحدكم مادحا لا محالة فليقل: أحسب كذا وكذا إن كان يرى أنه كذلك وحسيبه الله، ولا يُزكَّى على الله أحد».
Abu Bakrah (may Allah be pleased with him) reported that a man was mentioned in the presence of the Prophet (may Allah's peace and blessings be upon him) and another man praised him. So the Prophet (may Allah's peace and blessings be upon him) said: “Woe unto you! You have cut the neck of your companion,” repeating it several times. Then he said: “If one of you has to praise (another), let him say: ‘I reckon him to be as such and such' if he sees him to be like that, and Allah is the One Who will take account of him. No one can testify the purity of others against Allah."
Explanation
The Hadīth carries some instructions from the blessed Sunnah. The Muslim should avoid exaggeration when praising others, as pride and conceit are one of the Satan's gateways. Praising and commending people excessively may make the praised one overwhelmed with delusion and arrogance and he becomes ruined. Therefore, a Muslim should be moderate when praising and lauding others, and leave the realities of people to Allah, the Exalted, Who is fully aware of secrets of the souls.
Source · Narrated by Bukhari & Muslim
From the Hadith Encyclopedia (hadeethenc.com).