How should the Imam act if he loses his ablution during prostration?

The Imam must withdraw immediately if his ablution (Wudu') becomes invalid. It is sunnah for him to appoint one of the congregants to complete the prayer with them, especially if an excuse arises that prevents him from completing it, such as having a ritual impurity (hadath), or severe nosebleed, or remembering a najasah (impurity) on his body or clothes, or fearing the loss of property or life, or being unable to perform a pillar (rukn) of the prayer.