What is the jurisprudential ruling when the regular Imam arrives during the performance of the prayer, or after it, if another person has already stepped forward to lead the congregants in prayer?

The designated Imam should not intentionally delay beyond the agreed-upon time for the iqamah, as this causes difficulty and hardship for the worshippers. However, if he is delayed but arrives before someone else steps forward, he has a greater right to lead the prayer, and it is not permissible for anyone else to lead over him except with his permission. Scholars have emphasized the strictness regarding someone leading the prayer over the designated Imam. If he is delayed and is nearby, a messenger should be sent to him for him to attend or to give permission to someone else. If he is far away or cannot be found, and it is known from his good character that he would not be offended by someone else leading, then it is recommended for the congregation to put forward someone suitable. If they fear his displeasure or discord, they should wait for him as long as there is no fear of the prayer time expiring; otherwise, they should pray.