On it being forbidden to get ahead of the Imam in coming up from bowing or prostration

Riyad as-Salihin (The Meadows of the Righteous)

by Imam Nawawi

337. Chapter: On it being forbidden to get ahead of the Imam in coming up from bowing or prostration

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1751. Abu Hurayra reported that the Prophet, may Allah bless him and grant him peace, said, "Do not those of you who raise their heads before the Imam fear lest Allah turn their heads into donkey-heads or that Allah will make their shape that of a donkey?" [Agreed upon]