Hadith: When you see those who praise others, throw dust upon their faces

عن المقداد رضي الله عنه :أن رجلا جعل يمدح عثمان رضي الله عنه فعَمِدَ المقداد، فجَثَا على ركبتيه، فجعل يَحْثُو في وجهه الحَصْبَاءَ. فقال له عثمان: ما شأنك؟ فقال: إن رسول الله صلى الله عليه وسلم قال: «إذا رأيتم المَدَّاحِينَ، فاحْثُوا في وجوههم التراب».
[صحيح] - [رواه مسلم]

Al-Miqdād (may Allah be pleased with him) reported that a person began to praise ‘Uthmān (may Allah be pleased with him). So Al-Miqdād knelt down and threw gravel on his (the flatterer's) face. Thereupon, ‘Uthmān said: "What is the matter with you?" He said: "The Messenger of Allah (may Allah's peace and blessings be upon him) said: 'When you see those who praise others, throw dust upon their faces.'"
Sahih/Authentic. - [Muslim]

Explanation

Al-Miqdād (may Allah be pleased with him) reported that a man was exaggerating in his praise of ‘Uthmān (may Allah be pleased with him). Al-Miqdād sat on his knees, gathered up small stones, and began throwing them at the face of the flatterer. ‘Uthmān asked him why he did that, so he informed him that the Prophet (may Allah's peace and blessings be upon him) ordered that when we see someone who showers praise upon others, we should throw dust at their faces.