Is there a period after which a traveler must complete his prayer?

Question:
If an employee is assigned to a distance where shortening the prayer is permitted, or a distance where the prayer is shortened, for a period of one or two weeks, meaning he knows approximately how long he will remain in the place of assignment, is it permissible for him to shorten the prayer? And is there a period after which, if he stays or knows he will stay, he must complete it?

Answer:
If he knows that he will stay for more than four days, he must complete the prayer according to the majority, according to most scholars. If he knows that he will reside for more than four days, he must complete the prayer according to most scholars of knowledge. Some scholars said: if the period is fifteen days. Some said nineteen days. Some said twenty days. If he resides for this period, he shortens the prayer. And if he knows that he will reside for more than that, he completes four rak'ahs.
In any case, if he knows that he will reside for more than four days, the safest course for him is to complete the prayer, so that he is safe from blame. But if he does not know, whether he will stay four days, three, five, six, or ten, and he has no certainty, then he prays shortened, he prays two by two, because he is a traveler and does not know when his period will end. Like the one who came to fight enemies, or came for a dispute, and does not know when it will end, or a need he is seeking from a person, and does not know when it will end. This person does not have a known period of residence; he has the ruling of a traveler.
But if he is alone, he does not pray alone; he prays with the people and completes four rak'ahs. He prays with the congregation; he does not pray one. But if he has brothers and companions who pray with him, they have a choice. If they wish, they pray alone two by two, shortened. And if they wish, they pray with the people, combine them, and complete four rak'ahs.