Sahih Adab al-Mufrad

Ata bin Abi Rabah narrates that a man was praising another person in the presence of Sayyiduna Ibn Umar (may Allah be pleased with them). So Sayyiduna Ibn Umar (may Allah be pleased with them) took some soil and began to throw it towards his (the praiser’s) mouth and said: The Messenger of Allah (peace and blessings be upon him) said: “When you see those who praise others, throw dust in their faces.”