What is the ruling on someone who intended to combine the Dhuhr and Asr prayers with an early combination (taqdim), then joined the congregational prayer for Asr with the intention of Dhuhr, and is it permissible for him to complete the Asr prayer thereafter?

It is permissible to perform the Dhuhr prayer behind an Imam who is praying Asr, as the validity of the prayer is not affected by the difference in intention between the Imam and the worshipper, according to many scholars. If a congregation is found, a person can pray with it, even if they pray one of the prayers in congregation and the other with a different congregation, or alone.