مسائل المنتخبه (Articles Of Islamic Acts) - الخوئي، السيد أبوالقاسم - الصفحة ٣٠٨ - Congregational Prayers

crosses his mind) he is in the condition which is the obligation of a follower e.g. if he is listening to Surah al-Hamd and surah of the Imam, he should end his prayers with the congregation. but if at the time of having doubt he is busy in an act which is the obligation of both himself and the Imam (e.g. if he is in bowing or prostration posture) he should end his prayers with the intention of individual prayers.
١٤٣٢. If while offering the prayer the follower wishes to make intention of individual prayer, and he did not have such f intention from the very outset, there is no harm in it. However, if this was his intention from the very beginning, it is difficult that this act of his is in order.
١٤٣٣. If the follower makes an intention of individual prayers after the Imam has recited Surah al-Hamd and surah, he should. on the basis of obligatory precaution, recite entire Surah al- Hamd and surah, and if he makes the intention of individual prayers before (the Imams) ending Surah al-Hamd and surah, it is necessary that he recite, the portion. which the Imam has recited.
١٤٣٤. If a person makes the intention of individual prayers during the congregation prayers, he cannot make the intention of congregational prayers again. Rather,if he is undecided as to whether or not he should make the intention of individual prayers, and eventually decides to end the prayers with congregation. it is difficult to say that his congregational prayers is in order.
١٤٣٥. It a person doubts whether or not he has made intention of individual prayers during the congregational prayers. he should consider that he has not made the intention of individual prayers:
١٤٣٦. If a person follows the Imam at the time when the Imam is in bowing state and participates in the bowing of the Imam, his prayers is in order. though the recitation by the Imam may have come to an end, and it will be treated as one