The Ruling on a Traveler Praying Behind a Resident

Question:
He says: Honorable Shaykh, may Allah grant you success. A person who is traveling prayed behind a resident and caught up with him for the last two rak'ahs, so he shortened the prayer with him. What is the ruling on this prayer, and on the past prayers in which he used to do this?

Answer:
The prayer is not valid. If one follows an imam who completes the prayer, it is obligatory for him to complete it in accordance with his imam. The Messenger of Allah (peace and blessings be upon him) said: "The imam is appointed to be followed, so do not differ with him." Also, the Companions in Mina prayed behind 'Umar ibn al-Khattab, the Commander of the Faithful (may Allah be pleased with him), while he was completing the prayer, so they completed it, even though they held that shortening was the ruling. They held that shortening was the ruling, but they completed it in accordance with the imam for the sake of unity of word and avoiding division. When I think it was Ibn 'Abbas who was asked, "Why does the traveler complete the prayer behind the resident?" he said, "That is the Sunnah, O my son. The Sunnah is this: the Sunnah of the Messenger of Allah (peace and blessings be upon him)." Yes, so his prayer is not valid, and he must repeat the prayers. Yes.