What is the ruling on the prayer of the congregants if the imam remembers after the prayer that he did not wipe his head during ablution?

If the Imam remembers after the prayer that he did not wipe his head during ablution, his prayer is invalid, and he must repeat ablution and prayer, especially if the continuity (muwalat) in ablution is considered obligatory. As for the prayer of the congregants, it is valid according to the preponderant opinion, because the Companions, such as Umar, Uthman, Ali, and Ibn Umar – may Allah be pleased with them – repeated their prayers but did not order the congregants to repeat theirs when it was discovered that the Imam had led them in prayer while in a state of ritual impurity. However, if it is merely a doubt after the prayer about wiping the head, it should not be given attention.