Mujahid (may Allah have mercy on him) narrates from Abu Ma'mar (may Allah have mercy on him) that a man stood up and began praising one of the rulers, so al-Miqdad (may Allah be pleased with him) began throwing dust in his face, and said that the Messenger of Allah (peace and blessings be upon him) ordered us: "That we throw dust in the faces of those who praise (others excessively)."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الشهادات / 21137