What is the ruling on the prayer of one who intended to pray Asr inadvertently while leading the people in Dhuhr prayer, then intended to discontinue the prayer and pronounced the Takbir for Ihram again with the intention of leading the Dhuhr prayer, and what is the ruling on the prayer of the congregants behind him, and what is required of the Imam if such a situation occurs to him?

Your prayer and the prayers of the congregants are valid, as they were unaware of the Imam's condition and believed his prayer to be valid. Your interruption of the prayer and then your return as Imam does not invalidate it, for it is permissible for the congregants to complete their prayers individually or to appoint a new Imam if the original Imam's prayer becomes invalid. Similarly, it is permissible for the regular Imam to step forward to lead the people in prayer if he arrives late, and the Imam who began leading them then becomes a congregant, just as the Prophet, peace and blessings be upon him, did when Abu Bakr led the people in prayer. If the Imam knows that he did not intend the obligatory prayer, he should interrupt his prayer and inform the congregants so that they can restart the prayer with him, and there is no blame on him for that. If he fears causing confusion, he may appoint someone else to complete the prayer with the people, and he himself becomes a congregant.