What does the imam do if he breaks his ritual purity during the prayer?

Question:
If the imam breaks his ritual purity while he is in prayer and there is a congregation behind him, what should he do at that time?

Answer:
If he breaks his ritual purity, he should step aside and appoint one of them to lead the people in prayer, completing the prayer for them. He should speak and say, “Step forward, so-and-so.” He should choose the most suitable person behind him and say, “Step forward and complete the prayer for the people; complete the people’s prayer.” This is the correct course of action, and it is the most correct, and it is the stronger of the scholars’ opinions.
If he had entered the prayer without being in a state of ritual purity and then became aware of it, he should appoint someone to complete the prayer with them. If he starts a new prayer with them and prays from the beginning, there is no harm, but the better and stronger view is to build upon what has already passed. This is why, when 'Umar ibn al-Khattab (may Allah be pleased with him) was stabbed while he was leading the people in prayer, he appointed 'Abd al-Rahman ibn 'Awf, who led them to complete the Fajr prayer without breaking it.
Q: Does he appoint someone before he breaks his ritual purity, or when he breaks it?
The Shaykh: This has two cases: One is that he feels the urge and is unable to hold it in because it distracts him, so he appoints someone before he breaks his ritual purity. If he breaks his ritual purity and the urge overtakes him—meaning the urge overcame him and he relieved himself—he appoints him after that. It is all the same, and there is no blame.