What should one do who intended to pray Dhuhr, then remembered during the prayer that he had already prayed it, and that the prayer he is currently praying is Asr? Should he say the tasleem and renew his intention, or should he renew his intention during the prayer?

The intention (niyyah) for a specific prayer is one of its pillars. The prayer must be specified in the heart at the time of intention, as the Prophet, peace and blessings be upon him, said: "Indeed, actions are by intentions, and for every person is what he intended." One is not required to verbalize the intention. If a worshiper does not specify the prayer in their intention, they must interrupt the prayer and begin anew with the intention for the present prayer. If they continue their prayer without specifying, they must repeat it. The intention must be made at the beginning of the prayer (at the time of takbirat al-ihram), not afterwards. It is not permissible to change the intention during the prayer from one obligatory prayer to another. Whoever does so has invalidated their prayer and must restart it.