Sahih al-Bukhari 691
Sahih al-Bukhari · Book 10: Call to Prayers (Adhaan) · The sin of the one who raises his head before the Imam (raises his head)
Narrated Abu Huraira:
حَدَّثَنَا حَجَّاجُ بْنُ مِنْهَالٍ ، قَالَ حَدَّثَنَا شُعْبَةُ ، عَنْ مُحَمَّدِ بْنِ زِيَادٍ ، سَمِعْتُ أَبَا هُرَيْرَةَ ، عَنِ النَّبِيِّ صلى الله عليه وسلم قَالَ " أَمَا يَخْشَى أَحَدُكُمْ ـ أَوْ لاَ يَخْشَى أَحَدُكُمْ ـ إِذَا رَفَعَ رَأْسَهُ قَبْلَ الإِمَامِ أَنْ يَجْعَلَ اللَّهُ رَأْسَهُ رَأْسَ حِمَارٍ أَوْ يَجْعَلَ اللَّهُ صُورَتَهُ صُورَةَ حِمَارٍ " .
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?"