Answered by Shaykh Amjad Rasheed
What is the correct way for a latecomer to complete his prayer if he joins during the third rak’ah of a four-rak’ah prayer? When should he sit for the tashahhud and when shouldn’t he? When should he recite a sura after the fatiha and when shouldn’t he? What should he recite while the imam is sitting for the tashahhud?
A. It is obligatory for a late follower to follow the imam’s movements in prayer. If, as was mentioned in the question, he joins during the third rakah [h: i.e. during or before the bowing (ruku) of the third rakah], it is obligatory for him to recite the fatiha [h: if he catches enough of the imam’s standing to be able to recite all of the fatiha, he must recite all of it; otherwise, he must recite what he can and follow the imam in bowing]. It is recommended for him to recite some Qur’an after [m: the fatiha] and before the imam’s bowing if the [m: imam’s] standing lasts long enough. He then bows and prostrates with the imam, and follows him in standing for the fourth rakah. He recites the fatiha and some Qur’an, as before, and performs the remaining integrals with the imam. When the imam sits for the tashahhud, the latecomer also sits and recites the tashahhud with him. When the imam gives salams, the latecomer rises to complete his prayer, which consists of two rakahs in this case. He recites the fatiha in these two [m: rakahs]. It is not recommended for him to recite any Qur’an after the fatiha if he did so during the first two [m: rakahs], since whatever a latecomer catches of the imam’s prayer is considered the beginning of his own prayer. As for if he didn’t recite [m: Qur’an after the fatiha] during the the first two rakahs, then he does so in the last two. He then bows, prostrates, sits for the tashahhud, recites it, and gives salams.
(Translated by Moustafa Elqabbany and Hamza Karamali)