And according to another opinion: It does not become invalid; because it is a minor interruption, similar to if he performed the ablution. If he joins the prayers at the time of the second, separating them is permissible; because once he has performed the first, the second is in its own time and does not cease to be a performed prayer (ada') due to delaying it (51). There is another opinion stating that continuity (mutaba'a) is a condition; because the reality of joining is the combining of one thing with another, and this does not occur with separation. The first opinion is more correct; because the first prayer, once performed correctly, is not invalidated by anything that occurs after it, and the second one does not occur except in its own time.

Section: Whenever one joins prayers at the time of the first, the existence of the excuse that permits it must be considered at the moment of commencing the first, finishing it, and commencing the second. Thus, whenever the excuse ceases during one of these three, joining is not permitted. If the rain stops during the first, then returns before finishing it, or ceases after the opening Takbir of the second, joining is permitted, and its cessation has no effect; because the excuse existed at the time of the intention, which is at the moment of the opening Takbir of the first, and at the time of joining, which is at the end of the first and the beginning of the second, so its absence at other times does not matter. As for the traveler, if he intends to reside during the first prayer, the joining and the shortening (qasr) are interrupted, and he is obligated to perform the full prayer. If he returns and intends to travel, he is not permitted to use the concessions until he departs from the city he is in. If he intends to reside after the opening Takbir of the second, or if his ship enters his home city during it, it is possible that he completes it, and it is valid by analogy to the cessation of rain. Some of the followers of Al-Shafi'i said: This is what the school of Al-Shafi'i necessitates. It is also possible that it turns into a supererogatory prayer (nafl) and the joining becomes invalid; because it is one of the travel concessions, and it becomes invalid (52) due to that, like shortening the prayer and wiping over the socks (mas'h), and because its condition ceased during it, similar to the rest of its conditions. It differs from the cessation of rain in two aspects: Firstly, the cessation is not certain, due to the possibility of its return during the prayer. Secondly, it is replaced by another permissible excuse, which is mud, unlike our case. The same ruling applies to the sick person who recovers and whose excuse ceases during the second prayer (53). As for if...