(25) باب النَّهْىِ عَنْ سَبْقِ الإِمَامِ، بِرُكُوعٍ أَوْ سُجُودٍ وَنَحْوِهِمَا
Abu Huraira reported:
The Messenger of Allah (ﷺ) said: Does the man who lifts his head ahead of the Imam (from prostration) not fear that Allah may change his head into the head of an ass?
Reference: Sahih Muslim 427 a
In-book reference: Book 4, Hadith 125
USC-MSA web (English) reference(deprecated numbering scheme): Book 4, Hadith 859