What is the ruling on an imam who realizes during the prayer that he is not in a state of ritual purity?

The questioner : The questioner asks: What should be done if the imam’s ablution is broken, or if he remembers that he is not in a state of purity while he is in prostration?

The Shaykh : The question heard is: What should be done if the imam’s ablution is broken during the prayer, or if he remembers that he was not in a state of purity? The action in this case is that he should leave the prayer and instruct one of the ma'mums (those praying behind him) behind him to complete the prayer in congregation. If we assume that he remembers while he is in the third rak'ah of the Zuhr prayer that he is not in a state of purity.
Then it is obligatory for him to leave, and it is not permissible for him to complete the prayer without purity. One of the ma'mums behind him takes over to complete the prayer. How much is left for them? He is in the third. He remembered while in the third, so the last rak'ah and the remainder of the third are left for them, is that right? Good.
If he does not remember until after the taslim. Hmm? The prayer is invalid, but the prayer of the ma'mums is valid, not invalid. Yes.
The apparent ruling is that during the prayer, even while he is in prostration, he stands up from his prayer and leaves. The ma'mums say, “Stand up from prostration and complete it with them, O so-and-so.”