on rising from rukū‘, while the followers in this last case say in a low voice, Rabba-nā wa la-kal ḥamd. The dkikr in rukū‘ and sajdah and the sitting posture is repeated in a low voice by the Imām, as well as those who follow him.
If a mistake is made in prayer, or the worshipper is doubtful about the number of rak‘ahs, he adds, what is called, sajdah sahw,(sahw meaning mistake) at the close of prayer, just before the taslīm. The sajdah sahw consists in performing a double prostration like the ordinary prostration in prayer. If the Imām has made a similar mistake, he, along with the whole congregation, performs sajdah sahw.
A person who comes in late and joins the congregational service when it has already started, must, if he has missed one or more rak‘ahs, complete the number after the Imām has finished. A rak‘ah is deemed to have been completed when a person joins the rukū‘, though he may have missed the qiyām.
If one is on a journey,48 the prayers are shortened. The sunnahs are all dropped with the exception of the two of the morning prayer, and the number of obligatory rak‘ahs in the Ẓuhr, ‘Aṣr and ‘Ishā’ prayers, which is four ordinarily, is reduced to two. In addition to this, the man who is journeying is allowed to combine the Ẓuhr and ‘Aṣr prayers and also the Maghrib and ‘Ishā’ prayers. The witr of the ‘Ishā’ prayer are also retained. If a man who is on a journey is chosen to lead the prayers, he shortens the prayers, while such of the followers who are not on a journey complete the number of rak‘ahs; but if the Imām is not on a journey, while some or all of the followers are, the latter do not shorten the prayer.
48 There is some difference of opinion as to whether it is necessary that the journey should extend over a certain specified distance or a certain specified time. But the best judge on this matter is the person concerned. A time-limit of a day and a night as the minimum is favoured.