What are the situations in which a person invalidates another's prayer?

Scholars have differed on the connection between the prayer of the congregant and the prayer of the Imam, holding three opinions: 1. There is no connection between them, and each individual prays for himself (this is generally the original view of the Shafi'i school). 2. The congregant's prayer is bound by and dependent on the Imam's prayer, so any flaw in the Imam's prayer extends to the congregant's prayer (this is the view of Abu Hanifa and a narration from Ahmad). 3. The congregant's prayer is bound by the Imam's prayer, but deficiencies only extend to it if there is no excuse for both (this is the view of Malik, Ahmad, and others).

The last opinion is the most balanced and aligns with what has been narrated from the Companions, as the invalidation of the congregant's prayer is not necessarily required merely by the invalidation of the Imam's prayer if the congregant has performed his prayer with all its conditions and pillars. This is supported by the hadith: "They pray with you, and if they are correct, then it is for you and for them; and if they err, then it is for you and against them."

So, if the Imam's prayer becomes invalid due to a reason specific to him, such as forgetting his purification, the congregant's prayer does not become invalid.

However, if the Imam's prayer becomes invalid due to an apparent reason that is not hidden from the congregants, and they continue to follow him, or if something that breaks the prayer passes between the Imam and his sutrah (such as a woman, a donkey, or a black dog), then the congregant's prayer becomes invalid.