The Prophet ﷺ said, "Isn't he who raises his head before the Imam afraid that Allah may transform his head into that of a donkey or his figure (face) into that of a donkey?"  

عَنِ النَّبِيِّ ﷺ قَالَ أَمَا يَخْشَى أَحَدُكُمْ أَوْ لاَ يَخْشَى أَحَدُكُمْ إِذَا رَفَعَ رَأْسَهُ قَبْلَ الإِمَامِ أَنْ يَجْعَلَ اللَّهُ رَأْسَهُ رَأْسَ حِمَارٍ أَوْ يَجْعَلَ اللَّهُ صُورَتَهُ صُورَةَ حِمَارٍ