As for the slave and the traveller, the sound view is that the Friday Prayer is established through them, and that they may validly serve as its imams and deliver its sermons as well. For there is no evidence for the view that this is invalid. The slave is legally accountable, and the traveller is legally accountable. How then can it be said that if a slave prays the Friday Prayer behind an imam, it is valid, but if he himself is the imam, it is invalid? No meaningful distinction is apparent. Nor is the claim—that his prayer is valid merely as a follower, and that what is not established independently may be established dependently—acceptable in every case.
“Whoever is excused from it due to an excuse, it becomes obligatory upon him if he attends, and it is established through him, …”
His statement, “Whoever is excused from it,” means: from the Friday Prayer.
His statement, “due to an excuse,” means such as illness.
His statement, “it becomes obligatory upon him and is established through him,” means that if he attends it, it becomes obligatory upon him and is established through him. This is because he is among those for whom it is obligatory, though attendance has been waived for him due to the excuse. Once he attends, the obligation becomes binding.
An example of this is a sick person for whom the Friday Prayer has been waived because of illness, but who bears the hardship and attends the Friday Prayer. It is then established through him: he is counted among the forty, may validly serve as imam, and may deliver its sermon. This is because he is eligible for the obligation, though there is a factor preventing the obligation from applying to him. There is a difference between someone who lacks a condition that makes the obligation binding and someone in whom a factor preventing it is present. One who lacks a condition for obligation is not eligible for the act of worship in the first place, whereas one in whom a factor preventing obligation is present is, in principle, eligible for it. Thus, once he reaches the place where the Friday Prayer is held, the factor preventing the obligation ceases, because that factor was the hardship of reaching the mosque. He is now among those for whom it is obligatory; it therefore becomes binding upon him, is established through him, and he may validly lead it in prayer.