Thus, the following of an obligatory-prayer performer by one performing a supererogatory prayer is permissible, as previously mentioned.

Section: If a traveler leads other travelers in prayer, and he forgets, performing it in full, then his prayer and their prayer are valid, and no prostration for forgetfulness (sujud al-sahw) is required for that. This is because it is an addition the deliberate performance of which does not invalidate the prayer, so prostration for its forgetfulness is not obligatory, similar to additional utterances, such as reciting while in prostration or sitting. Is prostration for it prescribed? This is a matter of two reported views regarding the aforementioned additions. Ibn Aqil chose the view that it does not require prostration, because he performed the essential components and thus did not need compensation. The reason for its prescription is that this is an addition that diminishes the excellence and impairs the perfection [of the prayer], so it resembles reciting in other than its proper place, or reciting a surah in the last two rak'ahs. If the Imam remembers after rising to the third rak'ah, he is not required to complete the prayer, and he has the option to sit down, for what necessitates completion is his intention or following a resident, and neither of these has occurred. If the follower knows that his rising was due to forgetfulness and they glorified Allah (tasbih) to him, they are not obliged to follow him, because it is forgetfulness and following him in it is not required. They have the right to separate from him if he does not return, just as if he were to rise to a third rak'ah in the dawn prayer (fajr). If they follow him, their prayer is not invalidated; because it is an addition that does not invalidate the Imam's prayer, therefore the follower's prayer is not invalidated by following him in it, just like the additions of utterances. Furthermore, if they were to separate from the Imam and complete it, their prayer would be valid, so doing so while in agreement with him is even more appropriate. The Qadi said: Their prayer is invalidated because they added two rak'ahs intentionally. If they do not know whether he rose out of forgetfulness or intentionally, they must follow him and are not allowed to separate from him, because the rule of the obligation to follow is established and is not removed by doubt.

277 - Issue: He said: "And if a traveler intends to stay in a town for more than twenty-one prayers, he completes [the prayer]."

The well-known view from Ahmad, may Allah have mercy on him, is that the duration that obligates the traveler to complete the prayer by virtue of the intention to stay is that which is more than twenty-one prayers.