Does the imam have to tell the followers that he didn’t have wudu?

The Common Case

The imam does not have to inform them [that he was ritually impure] because their praying behind him is valid if they didn’t know that he was ritually impure.

The Exception

The exception to this rule is if the imam knows that he recited the Fatiha on behalf of one of the followers. This would occur if a follower entered [late], found the imam already bowing (ruku`), and bowed with him without reciting the Fatiha. In normal circumstances, this rak`a would have counted for the follower because the imam’s recital of the Fatiha would have sufficed on the follower’s behalf. However, when it becomes clear that the imam was actually ritual impure during this rak`a, then it becomes apparent that he could not validly recite the Fatiha on the follower’s behalf. It is then obligatory for the follower to perform a rak`a [in place of the one in which he didn’t recite the Fatiha because of joining the prayer late]. For this reason, it is obligatory for the imam [in this case] to inform him that he was ritually impure so that he can perform the rak`a, for this is an instance of commanding the right that is personally obligatory for him to perform. This is the fatwa of our Shaykh, Muhammad al-Khatib [may Allah preserve him and benefit us all through him].

– Amjad Rasheed

[Translated by Hamza Karamali]

السؤال : هل يجب على الإمام أن يخبر المأمومين بأنه كان محدثاً ؟ الجواب : لا يجب على الإمام إخبارهم بذلك ؛ لأن صلاتهم خلفه مع عدم علمهم بأنه محدث صحيحة ؛ إلا إن علم الإمام أنه قد تحمل عن بعض المأمومين فاتحة ، وذلك كأن دخل مأمومٌ فأدرك الإمامَ في الركوع فركع معه ولم يكن قد قرأ الفاتحة فركعته في الأصل صحيحة لأن الإمام قد تحمل الفاتحة عنه ، لكن لما تبين أن الإمام كان محدثاً في هذه الركعة ظهر أن تحمله للفاتحة عن هذا المأموم غيرُ صحيح فيجب على المأموم حينئذ أن يأتي بركعة ، فلذا يجب على الإمام أن يخبره بأنه كان محدثاً ليأتي بركعة ؛ لأنه أمر بالمعروف تعين عليه ، هذا ما أفتى به شيخنا محمد الخطيب .