The permissibility of a traveler completing his prayer when he prays behind a resident

A letter from Munir ibn Nuwar al-Atiwi from al-Saman, in which he says: I prayed the 'Asr prayer with the imam in the city of Riyadh while I was a traveler. I only caught one rak'ah with him, then I prayed one and said the taslim, because I shorten the prayer. When I finished, some of the brothers asked me: Why did you pray two and say the taslim? I told him: Because I am a traveler, and I had prayed the Zuhr prayer alone as two rak'ahs, and I caught one rak'ah with the imam, so I prayed the second and said the taslim. He said to me: It is not permissible; because if you did not catch the imam with the congregation and you entered the congregation, it is not permissible for you to shorten, and it is obligatory for you to follow the congregation whenever you find it. I complied with his ruling in this fatwa, but what should I do regarding the previous matters if this ruling is correct?
Answer: In the name of Allah, the Most Gracious, the Most Merciful. Praise be to Allah, and may peace and blessings be upon the Messenger of Allah, and upon his family and his companions, and whoever follows his guidance.
As for what follows: Yes, this fatwa is correct. If a traveler prays alone, he prays two, or if he prays with a group of travelers, he prays two with them. But if he prays with a resident—meaning the resident who prays four—he prays four with him and does not shorten. If he catches them in the prayer and bows with them for one rak'ah in the Zuhr, 'Asr, or 'Isha' prayer, he completes three so that he finishes four. If he catches him for one rak'ah in the Maghrib, he completes two so that he finishes the Maghrib as three. If he catches him for one rak'ah in the Jumu'ah or the Fajr, he prays a second rak'ah so that he completes it.
And this is authentic from the Prophet (peace and blessings be upon him) in the hadith of Ibn 'Abbas (may Allah be pleased with them both), where he was asked about a traveler who prays with the imam. He said: He prays four. If he prays with travelers, he prays two. The questioner asked him about that, and he said: This is the Sunnah. The questioner said to him: Muslim reported it in his Sahih, and Imam Ahmad (may Allah have mercy on him) reported it with a good chain of narration.
And this is the correct position: that a traveler does not shorten except if he is alone or with travelers. But if he prays with residents who pray four, he prays four with them, whether he joins from the beginning or in the middle. If he joins in the middle and then his imam says the taslim, he completes the four. This is what is obligatory.
As for the prayers you previously prayed where you prayed two while you were with the imam, if they were few, the safest course is to make them up. But if it has been a long time, perhaps Allah will forgive you, if Allah wills, because you prayed out of ignorance.
And the Prophet (peace and blessings be upon him), when he saw the one who prayed poorly, ordered him to repeat the current prayer and did not order him to make up the missed prayer, because of ignorance. So you are the same: if the prayers were few and you repeated them, that is good. Otherwise, there is nothing on you, because what is required is that you do what has reached you of Islamic legal knowledge. When the Islamic legal knowledge reached you and you complied, praise be to Allah. As for the past, we hope that Allah will forgive you, Glorified and Exalted is He.
And the most likely, and Allah knows best, is that there is nothing on you regarding the past; because you did it under the impression that you were on the right and the truth, and you had a doubtful matter regarding what is known for travelers, which is praying two. So you have a doubtful matter, and Allah forgives all of it, and there is no making up of what was missed, if Allah wills.
But in the future, if you meet the resident imams, pray four with them. And if you miss something, you complete four.
The presenter: Okay! Regarding a traveler who arrives in the city and wants to pray alone shortened, is that permissible for him, knowing that he hears the adhan and is close to the mosque and can catch the congregation?
The Shaykh: It is not permissible for him if he is alone; it is not permissible for him. Rather, he prays with the people; because the congregation is obligatory.
But if there are two or more, they have a choice. If they wish, they pray alone shortened, and if they wish, they pray with the imams in the mosques and complete four. Yes.