Sunan Abi Dawud, Book 2, Hadith 623 (USC-MSA) ⓘ
Abu Hurairah reported the Messenger of Allah as saying; Does he who raises his head while the Imam is prostrating not fear that Allah may change his head into a donkey’s or his face into a donkey’s face.
حَدَّثَنَا حَفْصُ بْنُ عُمَرَ، حَدَّثَنَا شُعْبَةُ، عَنْ مُحَمَّدِ بْنِ زِيَادٍ، عَنْ أَبِي هُرَيْرَةَ، قَالَ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم " أَمَا يَخْشَى - أَوْ أَلاَ يَخْشَى - أَحَدُكُمْ إِذَا رَفَعَ رَأْسَهُ وَالإِمَامُ سَاجِدٌ أَنْ يُحَوِّلَ اللَّهُ رَأْسَهُ رَأْسَ حِمَارٍ أَوْ صُورَتَهُ صُورَةَ حِمَارٍ " .
also referenced under: Hadith 623 (DarusSalam) & Hadith 623 (Hasan)