If a traveler catches up with the resident imam in the fourth rak'ah, is it permissible for him to perform a second rak'ah with the intention of shortening the prayer, or is it obligatory for him to complete the full prayer?

The questioner : In the name of Allah, the Most Gracious, the Most Merciful.
May Allah reward you. A traveler who is on his way wants to pray, so he joins a congregation praying the 'Asr prayer whose imam is a resident. He finds them in the fourth rak'ah. Does he complete the prayer as a four-rak'ah prayer after the imam's taslim, or does he perform one rak'ah with the intention of shortening?

The Shaykh : Yes, if you catch up with the imam in the last rak'ah, it is obligatory for you to complete four rak'ahs, due to the generality of the saying of the Prophet (peace and blessings be upon him and his family): , and because Ibn 'Abbas (may Allah be pleased with him and his father) was asked: Therefore, if you catch up with an imam who is praying four rak'ahs, even if it is during the tashahhud, and you join him, it is obligatory for you to complete four rak'ahs. If this questioner, for example, has already prayed two rak'ahs, then inform him that he must repeat the prayer now as four rak'ahs. Yes.