مسائل المنتخبه (Articles Of Islamic Acts) - الخوئي، السيد أبوالقاسم - الصفحة ٣١٢ - Congregational Prayers

and he should act according to the obligation of a person offering prayers individually.
١٤٥٣. If a person is satisfied that if he commences a surah or completes it, he will join the Imam in his bowing provided that the surah is not very long, it is better for him to commence the surah or to complete it, if he has already commenced it, and if the surah is too long the obligatory precaution is that he should not commence it, and if he has commenced it he should not complete it.
١٤٥٤. If a person is sure that if he recites the surah he will join the Imam in bowing and if he recites the surah and cannot join the Imam in bowing his congregational prayers is in order.
١٤٥٥. If the Imam is standing and the follower does not know in which unit he is, he can follow him, but he should recite Surah al-Hamd and surah with the intentionof complying with the orders of the Almighty Allah, though he may come to know after that the Imam was in the first or second unit.
١٤٥٦. If a person does not recite Surah al-Hamd and surah under the impression that the Imam is in the first or second unit and realizes after bowing that he was in the third or fourth unit his prayers is in order. However, if he realizes this before bowing he should recite Surah al-Hamd and surah and if he does not have sufficient time for this he should recite only Surah al-Hamd and should join the Imam in bowing and if.he cannot do so he should, on the basis of obligatory precaution, make an intention of individual prayers.
١٤٥٧. If a person recites Surah al-Hamd and surah under the impression that the Imam is in the third or fourth unit and realizes before bowing or thereafter that hewas in the first or second unit his (i.e. the followers) prayers is in order. and if he realizes this while reciting Surah al-Hamd and surah it is not necessary for him tocomplete them,
١٤٥٨. If a congregational prayers is established while a person