Abu Hurairah (May Allah be pleased with him) said:
The Prophet (ﷺ) said, "Does he who raises up his head before the Imam not fear that Allah will make his head that of a donkey or make his appearance similar to that of donkey?"[Al-Bukhari and Muslim]. (DE)
App reference (DE): Book 18, Hadith 241 (DE)
Arabic/English book reference (DE): Book 18, Hadith 1751 (DE)