What is the ruling on a traveler's prayer when he intends to pray Dhuhr shortened behind an Imam of Friday prayer, and is that permissible for him, and if his prayer is invalid, must he repeat it?

If a traveler attends the Friday prayer, the majority of scholars hold that it is not obligatory for him, and he is permitted to intend the Dhuhr prayer behind the Imam, praying it four rak'ahs because he is following a resident. Some scholars, however, are of the opinion that if a traveler attends the Friday prayer, it becomes obligatory upon him. Ibn 'Uthaymeen chose the view that it is obligatory upon him whenever he hears the second call to prayer, and that his intention for Dhuhr or delaying it is not valid. The correct view is that if a traveler prays Dhuhr behind someone praying Jumu'ah, his prayer is valid. However, it is more cautious for him to pray Jumu'ah to avoid disagreement and to gain reward.