If he appoints a traveler as a successor who was not with them in the prayer, it is permissible for him to perform the traveler's prayer, because he did not follow a resident.

Section: If a traveler enters into the opening takbir behind a resident, or one whom he strongly suspects is a resident, or one about whom he is unsure whether he is a resident or a traveler, it is binding upon him to complete the prayer, even if his Imam shortens it. This is because the fundamental rule is the obligation of the prayer in its entirety (four rak'ahs), and he does not have the intention of shortening it while in doubt regarding the obligation of completing it; thus, he is bound to complete it based on his intention. This is the school of al-Shafi'i. However, if he strongly suspects that the Imam is a traveler—due to seeing the outward appearance of travelers upon him and the signs of travel—then it is permissible for him to intend to shorten the prayer. If his Imam shortens it, he shortens it with him; if he completes it, he is bound to follow him. If he intends to complete it, he is bound to complete it, regardless of whether his Imam shortens it or completes it, based on his intention. If he intends to shorten the prayer and his Imam breaks his ablution before he becomes aware of his status, it is permissible for him to shorten the prayer, because the apparent situation is that his Imam is a traveler due to the presence of evidence for it, and the intention to shorten it has been made permissible for him based on this outward appearance. It is also possible that he is bound to complete it as a precaution.

Section: If a traveler performs the prayer of fear with travelers and divides them into two groups, then breaks his ablution before separating from the first group and appoints a resident as a successor, it becomes binding upon both groups to complete the prayer due to the existence of following a resident. [If this was after separating from the first, the second group completes it alone, due to their exclusivity in following the resident.] If the Imam was a resident and he appointed a traveler as a successor from among those who were with him in the prayer, then it is binding upon everyone to complete it, because the appointed successor has become bound to complete it by virtue of his following a resident, so he becomes like the resident. If he had not entered the prayer with him and his appointment took place before separating from the first group, it is binding upon them to complete it due to their following a resident, while the Imam and the second group shorten the prayer. If a successor is appointed after the second group has entered with him, it is binding upon everyone to complete it.