Should the congregants repeat their prayer if the Imam doubts the validity of his ablution after completing the prayer and informing them of that?

If the Imam doubts that he missed a part of his ablution after completing the act of worship, he should not pay attention to this doubt, and his prayer and the prayer of the congregants are valid. If he doubts the invalidation of his purification, he should build upon certainty, which is purification, and his prayer and the prayer of the congregants are valid. However, if the Imam is certain of the impurity (hadath) and doubts his purification, then his prayer is invalid, and he must repeat it, withdraw from the prayer, and appoint a successor.

Scholars differed regarding the validity of the congregants' prayer behind an Imam who knows his own impurity: The majority held that it is invalid. The Hanbalis distinguished between cases where the Imam knows his own impurity, in which case the congregants' prayer is invalidated, and where he is unaware of his own impurity, in which case only the Imam's prayer is invalidated, and the congregants' prayer remains valid. العلامة Al-Uthaymeen preferred the view that the congregants' prayer is valid in all cases, even if the Imam knows his own impurity, as long as the congregants are unaware of the Imam's impurity.

If the Imam remembers his impurity during the prayer, he must withdraw and appoint a successor. If he does not, the congregants have the choice between presenting one of them to complete the prayer or completing it individually. It is more prudent for the congregants in this case to repeat the prayer.