The Prophet (may Allah's peace and blessings be upon him) heard a man praising another and exaggerating in his praise, whereupon he said: You have ruined - or cut - the man's back.
Authentic hadithعن أبي موسى الأشعري - رضي الله عنه- قال: سمع النبي صلى الله عليه وسلم رجلا يُثْنِي على رجل ويُطْرِيهِ في المِدْحَةِ، فقال: «أَهْلَكْتُمْ -أو قَطَعْتُمْ- ظَهْرَ الرجل».
Abu Mūsa al-Ash‘ari (may Allah be pleased with him) reported: The Prophet (may Allah's peace and blessings be upon him) heard a man praising another and exaggerating in his praise, whereupon he said: ‘You have ruined - or cut - the man's back.
Explanation
The Prophet (may Allah's peace and blessings be upon him) heard a man praising someone else, and exaggerating in describing him with praiseworthy qualities that he did not possess. So, the Prophet (may Allah's peace and blessings be upon him) forbade him from that, and informed him that this could be a cause for that man's destruction, since it would lead him to be haughty and arrogant.
Source · Narrated by Bukhari & Muslim
From the Hadith Encyclopedia (hadeethenc.com).