Therefore, if a man leads a congregation whose regular imam normally leads them with a short recitation and brief bowing and prostration, but this man leads them with recitation, bowing, and prostration in accordance with the sunnah, then it is not permissible for any of them to separate, because this is not a valid excuse.

Another excuse is if a person is overcome by vomiting during the prayer and is unable to remain until the imam finishes; he may then shorten his prayer, leave, and depart.

Another excuse is if a person develops gas—wind in his stomach—and finds it difficult to remain with his imam. He may then separate, shorten his prayer, and depart.

Another excuse is if he is afflicted by an urgent need to urinate or defecate, such that he is restrained by urine or stool.

However, if it is assumed that he gains nothing by separating from the imam, because the imam is praying briefly, and even if he were to shorten it further than the imam's shortening he would not attain composure in the prayer, then it is not permissible for him to separate, because he gains nothing from this separation.

Another excuse is when the follower's prayer is shorter than the imam's prayer; for example, when one prays Maghrib behind someone praying Isha, according to the view that permits this. In that case, he may separate, recite the tashahhud, give the salām, and leave. Or, if he wishes to combine with the imam what remains of the Isha prayer, he may join him and then complete his prayer after the imam's salām. This view is one narration from Imam Ahmad (1), may Allah have mercy on him.