What is the expiation for an Imam leading a congregational prayer while in a state of ritual impurity (حدث), out of embarrassment to put forward one of the worshippers?

One must not surrender to shyness in matters of religion. Whoever experiences ritual impurity (hadath) or recalls having experienced it during prayer must interrupt the prayer to purify themselves. It is recommended for the Imam to appoint a successor. The questioner must repent and repeat the prayers in which he erred. The prayer of the congregants is not invalidated by the Imam's impurity if they were unaware of the invalidity of his prayer.