All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
If the Imaam (the person leading the prayer) remembers after the prayer that he was not in a state of purity, he is not obliged to inform the congregation about it, but he is obliged to purify himself and repeat the prayer. But the prayer of the congregations is valid.
For more benefit, please refer to Fatwa 90533.