The Prophet ﷺ said, "Does one of you not fear, when he raises his head before the imam, that Allah will turn his head into the head of a donkey, or that Allah will turn his form into the form of a donkey?"
عن النبي ﷺ قال: أما يخشى أحدكم- أو لا يخشى أحدكم- إذا رفع رأسه قبل الإمام أن يجعل الله رأسه رأس حمار، أو يجعل الله صورته صورة حمار.
Bukhari narrated it in the chapter on adhan (691) from Hajjaj bin Minhal, who said, Shubah narrated to us, from Muhammad bin Ziyad, I heard Abu Hurairah, and he mentioned the like of it. Muslim narrated it in the chapter on prayer (427) through several routes from Shubah, with the like of it. He also narrated it through the route of Rabi bin Muslim, from Muhammad bin Ziyad, and in it, "that Allah turn his face into the face of a donkey." Abu Dawud narrated it (623) from Hafs bin Umar, from Shubah, and in it, "if he raises his head while the imam is prostrating."