Some people of ḥadīth (such as al-Mulá ʿAlī al-Qārī, as-Suyūṭī and others) mentioned a story of a man who once travelled to Damascus in order to study ḥadīth from one of its famous teachers. So when he would study with this teacher there would be a veil placed between them, the student would never see the face of this teacher. As time passed the teacher notice the great enthusiasm of this student and decided to uncover the veil and show his face. “Be careful my son, that you do not proceed the Imām!” said the teacher. ‘When I came across the narration of not proceeding the Imām in prayer, I ignored it and didn’t give it any mind, I proceeded Imām in prayer and thus my face became as you see.”1 His face was that of a donkey.
Abu Hurayrah mentioned that the Prophet ﷺ said: “Does any of you not fear that if he raises his head before the Imām, that Allah ﷻ may turn his head into the head of a donkey, or that He ﷻ may change his figure into the figure of a donkey?” [Muslim no.427].